NAME¶
DBD::ODBC - ODBC Driver for DBI
VERSION¶
This documentation refers to DBD::ODBC version 1.37.
SYNOPSIS¶
use DBI;
$dbh = DBI->connect('dbi:ODBC:DSN', 'user', 'password');
See DBI for more information.
DESCRIPTION¶
Change log and FAQs¶
Please note that the change log has been moved to DBD::ODBC::Changes. To access
this documentation, use "perldoc DBD::ODBC::Changes".
The FAQs have also moved to DBD::ODBC::FAQ.pm. To access the FAQs use
"perldoc DBD::ODBC::FAQ".
Important note about the tests¶
Please note that some tests may fail or report they are unsupported on this
platform. Notably Oracle's ODBC driver will fail the "advanced"
binding tests in t/08bind2.t. These tests run perfectly under SQL Server 2000.
This is normal and expected. Until Oracle fixes their drivers to do the right
thing from an ODBC perspective, it's going to be tough to fix the issue. The
workaround for Oracle is to bind date types with SQL_TIMESTAMP. Also note that
some tests may be skipped, such as t/09multi.t, if your driver doesn't seem to
support returning multiple result sets. This is normal.
DBI attribute handling¶
If a DBI defined attribute is not mentioned here it behaves as per the DBI
specification.
ReadOnly (boolean)
DBI documents the "ReadOnly" attribute as being settleable and
retrievable on connection and statement handles. In ODBC setting ReadOnly to
true causes the connection attribute "SQL_ATTR_ACCESS_MODE" to be
set to "SQL_MODE_READ_ONLY" and setting it to false will set the
access mode to "SQL_MODE_READ_WRITE" (which is the default in ODBC).
Note: There is no equivalent of setting ReadOnly on a statement handle in
ODBC.
Note: See ODBC documentation on "SQL_ATTR_ACCESS_MODE" as
setting it to "SQL_MODE_READ_ONLY" does
not prevent your
script from running updates or deletes; it is simply a hint to the
driver/database that you won't being doing updates.
This attribute requires DBI version 1.55 or better.
Private attributes common to connection and statement
handles¶
odbc_ignore_named_placeholders
Use this if you have special needs (such as Oracle triggers, etc) where :new or
:name mean something special and are not just place holder names. You
must then use ? for binding parameters. Example:
$dbh->{odbc_ignore_named_placeholders} = 1;
$dbh->do("create trigger foo as if :new.x <> :old.x then ... etc");
Without this, DBD::ODBC will think :new and :old are placeholders for binding
and get confused.
odbc_default_bind_type
This value defaults to 0.
Older versions of DBD::ODBC assumed that the parameter binding type was 12
("SQL_VARCHAR"). Newer versions always attempt to call
"SQLDescribeParam" to find the parameter types but if
"SQLDescribeParam" is unavailable DBD::ODBC falls back to a default
bind type. The internal default bind type is "SQL_VARCHAR" (for
non-unicode build) and "SQL_WVARCHAR" (for a unicode build). If you
set "odbc_default_bind_type" to a value other than 0 you override
the internal default.
N.B If you call the "bind_param" method with a SQL type this
overrides everything else above.
odbc_force_bind_type
This value defaults to 0.
If set to anything other than 0 this will force bound parameters to be bound as
this type and "SQLDescribeParam" will not be used.
Older versions of DBD::ODBC assumed the parameter binding type was 12
("SQL_VARCHAR") and newer versions always attempt to call
"SQLDescribeParam" to find the parameter types. If your driver
supports "SQLDescribeParam" and it succeeds it may still fail to
describe the parameters accurately (MS SQL Server sometimes does this with
some SQL like
select myfunc(?) where 1 = 1). Setting
"odbc_force_bind_type" to "SQL_VARCHAR" will force
DBD::ODBC to bind all the parameters as "SQL_VARCHAR" and ignore
SQLDescribeParam.
Bare in mind that if you are inserting unicode data you probably want to use
"SQL_WVARCHAR" and not "SQL_VARCHAR".
As this attribute was created to work around buggy ODBC Drivers which support
SQLDescribeParam but describe the parameters incorrectly you are probably
better specifying the bind type on the "bind_param" call on a per
statement level rather than blindly setting "odbc_force_bind_type"
across a whole connection.
N.B If you call the "bind_param" method with a SQL type this
overrides everything else above.
odbc_force_rebind
This is to handle special cases, especially when using multiple result sets. Set
this before execute to "force" DBD::ODBC to re-obtain the result
set's number of columns and column types for each execute. Especially useful
for calling stored procedures which may return different result sets each
execute. The only performance penalty is during
execute(), but I didn't
want to incur that penalty for all circumstances. It is probably fairly rare
that this occurs. This attribute will be automatically set when multiple
result sets are triggered. Most people shouldn't have to worry about this.
odbc_async_exec
Allow asynchronous execution of queries. This causes a spin-loop (with a small
"sleep") until the ODBC API being called is complete (i.e., while
the ODBC API returns "SQL_STILL_EXECUTING"). This is useful,
however, if you want the error handling and asynchronous messages (see the
"odbc_err_handler" and
t/20SQLServer.t for an example of
this).
odbc_query_timeout
This allows you to change the ODBC query timeout (the ODBC statement attribute
"SQL_ATTR_QUERY_TIMEOUT"). ODBC defines the query time out as the
number of seconds to wait for a SQL statement to execute before returning to
the application. A value of 0 (the default) means there is no time out. Do not
confuse this with the ODBC attributes "SQL_ATTR_LOGIN_TIMEOUT" and
"SQL_ATTR_CONNECTION_TIMEOUT". Add
{ odbc_query_timeout => 30 }
to your connect, set on the "dbh" before creating a statement or
explicitly set it on your statement handle. The odbc_query_timeout on a
statement is inherited from the parent connection.
Note that internally DBD::ODBC only sets the query timeout if you set it
explicitly and the default of 0 (no time out) is implemented by the ODBC
driver and not DBD::ODBC.
Note that some ODBC drivers implement a maximum query timeout value and will
limit timeouts set above their maximum. You may see a warning if your time out
is capped by the driver but there is currently no way to retrieve the capped
value back from the driver.
Note that some drivers may not support this attribute.
See
t/20SqlServer.t for an example.
odbc_putdata_start
"odbc_putdata_start" defines the size at which DBD::ODBC uses
"SQLPutData" and "SQLParamData" to send larger objects to
the database instead of simply binding them as normal with
"SQLBindParameter". It is mostly a placeholder for future changes
allowing chunks of data to be sent to the database and there is little reason
for anyone to change it currently.
The default for odbc_putdata_start is 32768 because this value was hard-coded in
DBD::ODBC until 1.16_1.
odbc_column_display_size
If you ODBC driver does not support the SQL_COLUMN_DISPLAY_SIZE and
SQL_COLUMN_LENGTH attributes to SQLColAtrributes then DBD::ODBC does not know
how big the column might be. odbc_column_display_size sets the default value
for the column size when retrieving column data where the size cannot be
determined.
The default for odbc_column_display_size is 2001 because this value was
hard-coded in DBD::ODBC until 1.17_3.
odbc_utf8_on
Set this flag to treat all strings returned from the ODBC driver (except columns
described as SQL_BINARY or SQL_TIMESTAMP and its variations) as UTF-8 encoded.
Some ODBC drivers (like Aster and maybe PostgreSQL) return UTF-8 encoded data
but do not support the SQLxxxW unicode API. Enabling this flag will cause
DBD::ODBC to treat driver returned data as UTF-8 encoded and it will be marked
as such in Perl.
Do not confuse this with DBD::ODBC's unicode support. The
"odbc_utf8_on" attribute only applies to non-unicode enabled builds
of DBD::ODBC.
odbc_old_unicode
Defaults to off. If set to true returns DBD::ODBC to the old unicode behavior in
1.29 and earlier. You can also set this on the prepare method.
By default DBD::ODBC now binds all char columns as SQL_WCHARs meaning the driver
is asked to return the bound data as wide (Unicode) characters encoded in
UCS2. So long as the driver supports the ODBC Unicode API properly this should
mean you get your data back correctly in Perl even if it is in a character set
(codepage) different from the one you are working in.
However, if you wrote code using DBD::ODBC 1.29 or earlier and knew DBD::ODBC
bound varchar/longvarchar columns as SQL_CHARs and decoded them yourself the
new behaviour will adversely affect you (sorry). To revert to the old
behaviour set odbc_old_unicode to true.
You can also set this attribute in the attributes passed to the prepare method.
See the stackoverflow question at
<
http://stackoverflow.com/questions/5912082>, the RT at
<
http://rt.cpan.org/Public/Bug/Display.html?id=67994> and lastly a small
discussion on dbi-dev at
<
http://www.nntp.perl.org/group/perl.dbi.dev/2011/05/msg6559.html>.
odbc_describe_parameters
Defaults to on. When set this allows DBD::ODBC to call SQLDescribeParam (if the
driver supports it) to retrieve information about any parameters.
When off/false DBD::ODBC will not call SQLDescribeParam and defaults to binding
parameters as SQL_CHAR/SQL_WCHAR depending on the build type.
You do not have to disable odbc_describe_parameters just because your driver
does not support SQLDescribeParam as DBD::ODBC will work this out at the start
via SQLGetFunctions.
Note: disabling odbc_describe_parameters when your driver does support
SQLDescribeParam may prevent DBD::ODBC binding parameters for some column
types properly.
You can also set this attribute in the attributes passed to the prepare method.
This attribute was added so someone moving from freeTDS (a driver which does not
support SQLDescribeParam) to a driver which does support SQLDescribeParam
could do so without changing any Perl. The situation was very specific since
dates were being bound as dates when SQLDescribeParam was called and chars
without and the data format was not a supported date format.
Private methods common to connection and statement handles¶
odbc_getdiagrec
@diags = $handle->odbc_getdiagrec($record_number);
NOTE: This is an experimental method and may change.
Introduced in 1.34_3.
This is just a wrapper around the ODBC API SQLGetDiagRec. When a method on a
connection or statement handle fails if there are any ODBC diagnostics you can
use this method to retrieve them. Records start at 1 and there may be more
than 1. It returns an array containing the state, native and error message
text or an empty array if the requested diagnostic record does not exist. To
get all diagnostics available keep incrementing $record_number until
odbc_getdiagrec returns an empty array.
All of the state, native and message text are already passed to DBI via its
set_err method so this method does not really tell you anything you cannot
already get from DBI except when there is more than one diagnostic.
You may find this useful in an error handler as you can get the ODBC diagnostics
as they are and not how DBD::ODBC was forced to fit them into the DBI's
system.
NOTE: calling this method does not clear DBI's error values as usually happens.
odbc_getdiagfield
$diag = $handle->odbc_getdiagfield($record, $identifier);
NOTE: This is an experimental method and may change.
This is just a wrapper around the ODBC API SQLGetDiagField. When a method on a
connection or statement handle fails if there are any ODBC diagnostics you can
use this method to retrieve the individual diagnostic fields. As with
"odbc_getdiagrec" records start at 1. The identifier is one of:
SQL_DIAG_CURSOR_ROW_COUNT
SQL_DIAG_DYNAMIC_FUNCTION
SQL_DIAG_DYNAMIC_FUNCTION_CODE
SQL_DIAG_NUMBER
SQL_DIAG_RETURNCODE
SQL_DIAG_ROW_COUNT
SQL_DIAG_CLASS_ORIGIN
SQL_DIAG_COLUMN_NUMBER
SQL_DIAG_CONNECTION_NAME
SQL_DIAG_MESSAGE_TEXT
SQL_DIAG_NATIVE
SQL_DIAG_ROW_NUMBER
SQL_DIAG_SERVER_NAME
SQL_DIAG_SQLSTATE
SQL_DIAG_SUBCLASS_ORIGIN
DBD::ODBC exports these constants as 'diags' e.g.,
use DBD::ODBC qw(:diags);
Of particular interest is SQL_DIAG_COLUMN_NUMBER as it will tell you which bound
column or parameter is in error (assuming your driver supports it). See
params_in_error in the examples dir.
NOTE: calling this method does not clear DBI's error values as usually happens.
Private connection attributes¶
odbc_err_handler
NOTE: You might want to look at DBI's error handler before using the one
in DBD::ODBC however, there are subtle differences. DBD::ODBC's
odbc_err_handler is called for error
and informational diagnostics
i.e., it is called when an ODBC call fails the SQL_SUCCEEDED macro which means
the ODBC call returned SQL_ERROR (-1) or SQL_SUCCESS_WITH_INFO (1).
Allow error and informational diagnostics to be handled by the application. A
call-back function supplied by the application to handle or ignore messages.
The callback function receives four parameters: state (string), error (string),
native error code (number) and the status returned from the last ODBC API. The
fourth argument was added in 1.30_7.
If the error handler returns 0, the error is ignored, otherwise the error is
passed through the normal DBI error handling. Note, if the status is
SQL_SUCCESS_WITH_INFO this will
not reach the DBI error handler as it
is not an error.
This can also be used for procedures under MS SQL Server (Sybase too, probably)
to obtain messages from system procedures such as DBCC. Check
t/20SQLServer.t and
t/10handler.t.
$dbh->{RaiseError} = 1;
sub err_handler {
($state, $msg, $native, $rc, $status) = @_;
if ($state = '12345')
return 0; # ignore this error
else
return 1; # propagate error
}
$dbh->{odbc_err_handler} = \&err_handler;
# do something to cause an error
$dbh->{odbc_err_handler} = undef; # cancel the handler
odbc_SQL_ROWSET_SIZE
Setting odbc_SQL_ROWSET_SIZE results in a call to SQLSetConnectAttr to set the
ODBC SQL_ROWSET_SIZE (9) attribute to whatever value you set
odbc_SQL_ROWSET_SIZE to.
The ODBC default for SQL_ROWSET_SIZE is 1.
Usually MS SQL Server does not support multiple active statements (MAS) i.e.,
you cannot have 2 or more outstanding selects. You can set
odbc_SQL_ROWSET_SIZE to 2 to persuade MS SQL Server to support multiple active
statements.
Setting SQL_ROWSET_SIZE usually only affects calls to SQLExtendedFetch but does
allow MAS and as DBD::ODBC does not use SQLExtendedFetch there should be no
ill effects to DBD::ODBC.
Be careful with this attribute as once set to anything larger than 1 (the
default) you must retrieve all result-sets before the statement handle goes
out of scope or you can upset the TDS protocol and this can result in a hang.
With DBI this is unlikely as DBI warns when a statement goes out of scope with
outstanding results.
NOTE: if you get an error saying "[Microsoft][ODBC SQL Server
Driver]Invalid attribute/option identifier (SQL-HY092)" when you set
odbc_SQL_ROWSET_SIZE in the connect method you need to either a) upgrade to
DBI 1.616 or above b) set odbc_SQL_ROWSET_SIZE after connect.
In versions of SQL Server 2005 and later see "Multiple Active Statements
(MAS)" in the DBD::ODBC::FAQ instead of using this attribute.
Thanks to Andrew Brown for the original patch.
DBD developer note: Here lies a bag of worms. Firstly, SQL_ROWSET_SIZE is an
ODBC 2 attribute and is usally a statement attribute not a connection
attribute. However, in ODBC 2.0 you could set statement attributes on a
connection handle and it acted as a default for all subsequent statement
handles created under that connection handle. If you are using ODBC 3 the
driver manager continues to map this call but the ODBC Driver needs to act on
it (the MS SQL Server driver still appears to but some other ODBC drivers for
MS SQL Server do not). Secondly, somewhere a long the line MS decided it was
no longer valid to retrieve the SQL_ROWSET_SIZE attribute from a connection
handle in an ODBC 3 application (which DBD::ODBC now is). In itself, this
would not be a problem except for a minor bug in DBI which until release 1.616
mistakenly issued a FETCH on any attribute mentioned in the connect method
call. As a result, it you use a DBI prior to 1.616 and attempt to set
odbc_SQL_ROWSET_SIZE in the connect method call, DBI issues a FETCH on
odbc_SQL_ROWSET_SIZE and the driver manager throws it out as an invalid
attribute thus resulting in an error. The only way around this (other than
upgrading DBI) is to set odbc_SQL_ROWSET_SIZE AFTER the call to connect.
Thirdly, MS withdrew the SQLROWSETSIZE macro from the sql header files in MDAC
2.7 for 64 bit platforms i.e., SQLROWSETSIZE is not defined on 64 bit
platforms from MDAC 2.7 as it is in a "#ifdef win32" (see
http://msdn.microsoft.com/en-us/library/ms716287%28v=vs.85%29.aspx). Setting
SQL_ROWSET_SIZE still seems to take effect on 64 bit platforms but you can no
longer retrieve its value from a connection handle (hence the issue above with
DBI redundant FETCH).
odbc_exec_direct
Force DBD::ODBC to use "SQLExecDirect" instead of
"SQLPrepare"/"SQLExecute".
There are drivers that only support "SQLExecDirect" and the DBD::ODBC
do() override does not allow returning result sets. Therefore, the way
to do this now is to set the attribute odbc_exec_direct.
NOTE: You may also want to use this option if you are creating temporary objects
(e.g., tables) in MS SQL Server and for some reason cannot use the
"do" method. see
http://technet.microsoft.com/en-US/library/ms131667.aspx
<
http://technet.microsoft.com/en-US/library/ms131667.aspx> which says
Prepared statements cannot be used to create temporary objects on
SQL Server 2000 or later.... Without odbc_exec_direct, the temporary
object will disappear before you can use it.
There are currently two ways to get this:
$dbh->prepare($sql, { odbc_exec_direct => 1});
and
$dbh->{odbc_exec_direct} = 1;
NOTE: Even if you build DBD::ODBC with unicode support you can still not
pass unicode strings to the prepare method if you also set odbc_exec_direct.
This is a restriction in this attribute which is unavoidable.
odbc_SQL_DRIVER_ODBC_VER
This, while available via
get_info() is captured here. I may get rid of
this as I only used it for debugging purposes.
odbc_cursortype
This allows multiple concurrent statements on SQL*Server. In your connect, add
{ odbc_cursortype => 2 }.
If you are using DBI > 1.41, you should also be able to use
{ odbc_cursortype => DBI::SQL_CURSOR_DYNAMIC }
instead. For example:
my $dbh = DBI->connect("dbi:ODBC:$DSN", $user, $pass,
{ RaiseError => 1, odbc_cursortype => 2});
my $sth = $dbh->prepare("one statement");
my $sth2 = $dbh->prepare("two statement");
$sth->execute;
my @row;
while (@row = $sth->fetchrow_array) {
$sth2->execute($row[0]);
}
See
t/20SqlServer.t for an example.
In versions of SQL Server 2005 and later see "Multiple Active Statements
(MAS)" in the DBD::ODBC::FAQ instead of using this attribute.
odbc_has_unicode
A read-only attribute signifying whether DBD::ODBC was built with the C macro
WITH_UNICODE or not. A value of 1 indicates DBD::ODBC was built with
WITH_UNICODE else the value returned is 0.
Building WITH_UNICODE affects columns and parameters which are SQL_C_WCHAR,
SQL_WCHAR, SQL_WVARCHAR, and SQL_WLONGVARCHAR, SQL, the connect method and a
lot more. See "Unicode".
When odbc_has_unicode is 1, DBD::ODBC will:
- bind columns the database declares as wide characters as
SQL_Wxxx
- This means that UNICODE data stored in these columns will
be returned to Perl in UTF-8 and with the UTF-8 flag set.
- bind parameters the database declares as wide characters as
SQL_Wxxx
- Parameters bound where the database declares the parameter
as being a wide character (or where the parameter type is explicitly set
to a wide type - SQL_Wxxx) can be UTF-8 in Perl and will be mapped to
UTF-16 before passing to the driver.
- SQL
- SQL passed to the "prepare" or "do"
methods which has the UTF-8 flag set will be converted to UTF-16 before
being passed to the ODBC APIs "SQLPrepare" or
"SQLExecDirect".
- connection strings
- Connection strings passed to the "connect" method
will be converted to UTF-16 before being passed to the ODBC API
"SQLDriverConnectW". This happens irrespective of whether the
UTF-8 flag is set on the perl connect strings because unixODBC requires an
application to call SQLDriverConnectW to indicate it will be calling the
wide ODBC APIs.
NOTE: You will need at least Perl 5.8.1 to use UNICODE with DBD::ODBC.
NOTE: Binding of unicode output parameters is coded but untested.
NOTE: When building DBD::ODBC on Windows ($^O eq 'MSWin32') the WITH_UNICODE
macro is automatically added. To disable specify -nou as an argument to
Makefile.PL (e.g. "perl Makefile.PL -nou"). On non-Windows platforms
the WITH_UNICODE macro is
not enabled by default and to enable you need
to specify the -u argument to Makefile.PL. Please bare in mind that some ODBC
drivers do not support SQL_Wxxx columns or parameters.
UNICODE support in ODBC Drivers differs considerably. Please read the
README.unicode file for further details.
odbc_out_connect_string
After calling the connect method this will be the ODBC driver's out connection
string - see documentation on SQLDriverConnect.
odbc_version
This was added prior to the move to ODBC 3.x to allow the caller to
"force" ODBC 3.0 compatibility. It's probably not as useful now, but
it allowed get_info and get_type_info to return correct/updated information
that ODBC 2.x didn't permit/provide. Since DBD::ODBC is now 3.x, this can be
used to force 2.x behavior via something like: my
$dbh = DBI->connect("dbi:ODBC:$DSN", $user, $pass,
{ odbc_version =>2});
odbc_driver_complete
This attribute was added to DBD::ODBC in 1.32_2.
odbc_driver_complete is only relevant to the Windows operating system and will
be ignored on other platforms. It is off by default.
When set to a true value DBD::ODBC attempts to obtain a window handle and calls
SQLDriverConnect with the SQL_DRIVER_COMPLETE attribute instead of the normal
SQL_DRIVER_NOPROMPT option. What this means is that if the connection string
does not describe sufficient attributes to enable the ODBC driver manager to
connect to a data source it will throw a dialogue allowing you to input the
remaining attributes. Once you ok that dialogue the ODBC Driver Manager will
continue as if you specified those attributes in the connection string. Once
the connection is complete you may want to look at the odbc_out_connect_string
attribute to obtain a connection string you can use in the future to pass into
the connect method without prompting.
As a window handle is passed to SQLDriverConnect it also means the ODBC driver
may throw a dialogue e.g., if your password has expired the MS SQL Server
driver will often prompt for a new one.
An example is:
my $h = DBI->connect('dbi:ODBC:DRIVER={SQL Server}', "username", "password",
{odbc_driver_complete => 1});
As this only provides the driver and further attributes are required a dialogue
will be thrown allowing you to specify the SQL Server to connect to and
possibly other attributes.
odbc_batch_size
Sets the batch size for execute_for_fetch which defaults to 10. Bare in mind the
bigger you set this the more memory DBD::ODBC will need to allocate when
running execute_for_fetch and the memory required is max_length_of_pn *
odbc_batch_size * n_parameters.
odbc_array_operations
NOTE: this was briefly odbc_disable_array_operations in 1.35 and 1.36_1. I did
warn it was experimental and it turned out the default was too ambitious and
it was a poor name anyway. Also the default was to use array operations and
now the default is the opposite.
If set to true DBD::ODBC uses its own internal execute_for_fetch instead of
DBI's default execute_for_fetch. The default is false. Using the internal
execute_for_fetch should be quite a bit faster when using arrays of parameters
for insert/update/delete operations as batches of parameters are sent to the
database in one go. However, the required support in some ODBC drivers is a
little sketchy and there is no way for DBD::ODBC to ascertain this until it is
too late.
Please read the documentation on execute_array and execute_for_fetch which
details subtle differences in DBD::ODBC's implementation compared with using
DBI's default implementation. If these difference cause you a problem you can
set odbc_array_operations to false and DBD::ODBC will revert to DBI's
implementations of the array methods.
You can use the environment variable ODBC_DISABLE_ARRAY_OPERATIONS to switch
array operations on/off too. When set to 1 array operations are disabled. When
not set the default is used (which currently is off). When set to 0 array
operations are used no matter what. I know this is slightly counter intuitive
but I've found it difficult to change the name (it got picked up and used in a
few places very quickly).
Private statement attributes¶
odbc_more_results
Use this attribute to determine if there are more result sets available. SQL
Server supports this feature. Use this as follows:
do {
my @row;
while (@row = $sth->fetchrow_array()) {
# do stuff here
}
} while ($sth->{odbc_more_results});
Note that with multiple result sets and output parameters (i.e,. using
bind_param_inout), don't expect output parameters to written to until ALL
result sets have been retrieved.
Private statement methods¶
odbc_lob_read
$chrs_or_bytes_read = $sth->lob_read($column_no, \$lob, $length, \%attr);
Reads $length bytes from the lob at column $column_no returning the lob into
$lob and the number of bytes or characters read into $chrs_or_bytes_read. If
an error occurs undef will be returned. When there is no more data to be read
0 is returned.
NOTE: This is currently an experimental method and may change in the future
e.g., it may support automatic concatenation of the lob parts onto the end of
the $lob with the addition of an extra flag or destination offset as in DBI's
undocumented blob_read.
The type the lob is retrieved as may be overridden in %attr using "TYPE
=> sql_type". %attr is optional and if omitted defaults to
SQL_C_BINARY for binary columns and SQL_C_CHAR/SQL_C_WCHAR for other column
types depending on whether DBD::ODBC is built with unicode support.
$chrs_or_bytes_read will by the bytes read when the column types SQL_C_CHAR or
SQL_C_BINARY are used and characters read if the column type is SQL_C_WCHAR.
When built with unicode support $length specifes the amount of buffer space to
be used when retrieving the lob data but as it is returned as SQLWCHAR
characters this means you at most retrieve "$length/2" characters.
When those retrieved characters are encoded in UTF-8 for Perl, the $lob scalar
may need to be larger than $length so DBD::ODBC grows it appropriately.
You can retrieve a lob in chunks like this:
$sth->bind_col($column, undef, {TreatAsLOB=>1});
while(my $retrieved = $sth->odbc_lob_read($column, \my $data, $length)) {
print "retrieved=$retrieved lob_data=$data\n";
}
NOTE: to retrieve a lob like this you
must first bind the lob column
specifying BindAsLOB or DBD::ODBC will 1) bind the column as normal and it
will be subject to LongReadLen and b) fail odbc_lob_read.
NOTE: Some database engines and ODBC drivers do not allow you to retrieve
columns out of order (e.g., MS SQL Server unless you are using cursors). In
those cases you must ensure the lob retrieved is the last (or only) column in
your select list.
NOTE: You can retrieve only part of a lob but you will probably have to call
finish on the statement handle before you do anything else with that
statement. When only retrieving part of a large lob you could see a small
delay when you call finish as some protocols used by ODBC drivers send the lob
down the socket synchonously and there is no way to stop it (this means the
ODBC driver needs to read all the lob from the socket even though you never
retrieved it all yourself).
NOTE: If your select contains multiple lobs you cannot read part of the first
lob, the second lob then return to the first lob. You must read all lobs in
order and completely or read part of a lob and then do no further calls to
odbc_lob_read.
Private DBD::ODBC Functions¶
You use DBD::ODBC private functions like this:
$dbh->func(arg, private_function_name, @args);
GetInfo
This private function is now superceded by DBI's get_info method.
This function maps to the ODBC SQLGetInfo call and the argument should be a
valid ODBC information type (see ODBC specification). e.g.
$value = $dbh->func(6, 'GetInfo');
which returns the "SQL_DRIVER_NAME".
This function returns a scalar value, which can be a numeric or string value
depending on the information value requested.
SQLGetTypeInfo
This private function is now superceded by DBI's type_info and
type_info_all methods.
This function maps to the ODBC SQLGetTypeInfo API and the argument should be a
SQL type number (e.g. SQL_VARCHAR) or SQL_ALL_TYPES. SQLGetTypeInfo returns
information about a data type supported by the data source.
e.g.
use DBI qw(:sql_types);
$sth = $dbh->func(SQL_ALL_TYPES, GetTypeInfo);
DBI::dump_results($sth);
This function returns a DBI statement handle for the SQLGetTypeInfo result-set
containing many columns of type attributes (see ODBC specification).
NOTE: It is VERY important that the "use DBI" includes the
"qw(:sql_types)" so that values like SQL_VARCHAR are correctly
interpreted. This "imports" the sql type names into the program's
name space. A very common mistake is to forget the "qw(:sql_types)"
and obtain strange results.
GetFunctions
This function maps to the ODBC SQLGetFunctions API which returns information on
whether a function is supported by the ODBC driver.
The argument should be "SQL_API_ALL_FUNCTIONS" (0) for all functions
or a valid ODBC function number (e.g. "SQL_API_SQLDESCRIBEPARAM"
which is 58). See ODBC specification or examine your sqlext.h and sql.h header
files for all the SQL_API_XXX macros.
If called with "SQL_API_ALL_FUNCTIONS" (0), then a 100 element array
is returned where each element will contain a '1' if the ODBC function with
that SQL_API_XXX index is supported or '' if it is not.
If called with a specific SQL_API_XXX value for a single function it will return
true if the ODBC driver supports that function, otherwise false.
e.g.
my @x = $dbh->func(0,"GetFunctions");
print "SQLDescribeParam is supported\n" if ($x[58]);
or
print "SQLDescribeParam is supported\n"
if $dbh->func(58, "GetFunctions");
GetStatistics
This private function is now superceded by DBI's statistics_info
method.
See the ODBC specification for the SQLStatistics API. You call SQLStatistics
like this:
$dbh->func($catalog, $schema, $table, $unique, 'GetStatistics');
Prior to DBD::ODBC 1.16 $unique was not defined as being true/false or
SQL_INDEX_UNIQUE/SQL_INDEX_ALL. In fact, whatever value you provided for
$unique was passed through to the ODBC API SQLStatistics call unchanged. This
changed in 1.16, where $unique became a true/false value which is interpreted
into SQL_INDEX_UNIQUE for true and SQL_INDEX_ALL for false.
GetForeignKeys
This private function is now superceded by DBI's foreign_key_info
method.
See the ODBC specification for the SQLForeignKeys API. You call SQLForeignKeys
like this:
$dbh->func($pcatalog, $pschema, $ptable,
$fcatalog, $fschema, $ftable,
"GetForeignKeys");
GetPrimaryKeys
This private function is now superceded by DBI's primary_key_info
method.
See the ODBC specification for the SQLPrimaryKeys API. You call SQLPrimaryKeys
like this:
$dbh->func($catalog, $schema, $table, "GetPrimaryKeys");
data_sources
This private function is now superceded by DBI's data_sources
method.
You call data_sources like this:
@dsns = $dbh->func("data_sources);
Handled since 0.21.
GetSpecialColumns
See the ODBC specification for the SQLSpecialColumns API. You call
SQLSpecialColumns like this:
$dbh->func($identifier, $catalog, $schema, $table, $scope,
$nullable, 'GetSpecialColumns');
Handled as of version 0.28
ColAttributes
This private function is now superceded by DBI's statement attributes
NAME, TYPE, PRECISION, SCALE, NULLABLE etc).
See the ODBC specification for the SQLColAttributes API. You call
SQLColAttributes like this:
$sth->func($column, $ftype, "ColAttributes");
SQL_COLUMN_COUNT = 0
SQL_COLUMN_NAME = 1
SQL_COLUMN_TYPE = 2
SQL_COLUMN_LENGTH = 3
SQL_COLUMN_PRECISION = 4
SQL_COLUMN_SCALE = 5
SQL_COLUMN_DISPLAY_SIZE = 6
SQL_COLUMN_NULLABLE = 7
SQL_COLUMN_UNSIGNED = 8
SQL_COLUMN_MONEY = 9
SQL_COLUMN_UPDATABLE = 10
SQL_COLUMN_AUTO_INCREMENT = 11
SQL_COLUMN_CASE_SENSITIVE = 12
SQL_COLUMN_SEARCHABLE = 13
SQL_COLUMN_TYPE_NAME = 14
SQL_COLUMN_TABLE_NAME = 15
SQL_COLUMN_OWNER_NAME = 16
SQL_COLUMN_QUALIFIER_NAME = 17
SQL_COLUMN_LABEL = 18
Note:Oracle's ODBC driver for linux in instant client 11r1 often returns
strange values for column name e.g., '20291'. It is wiser to use DBI's NAME
and NAME_xx attributes for portability.
DescribeCol
This private function is now superceded by DBI's statement attributes
NAME, TYPE, PRECISION, SCALE, NULLABLE etc).
See the ODBC specification for the SQLDescribeCol API. You call SQLDescribeCol
like this:
@info = $sth->func($column, "DescribeCol");
The returned array contains the column attributes in the order described in the
ODBC specification for SQLDescribeCol.
Additional bind_col attributes¶
DBD::ODBC supports a few additional attributes which may be passed to the
bind_col method in the attributes.
DiscardString
See DBI's sql_type_cast utility function.
If you bind a column as a specific type (SQL_INTEGER, SQL_DOUBLE and SQL_NUMERIC
are the only ones supported currently) and you add DiscardString to the
prepare attributes then if the returned bound data is capable of being
converted to that type the scalar's pv (the string portion of a scalar) is
cleared.
This is especially useful if you are using a module which uses a scalars flags
and/or pv to decide if a scalar is a number. JSON::XS does this and without
this flag you have to add 0 to all bound column data returning numbers to get
JSON::XS to encode it is N instead of "N".
NOTE: For DiscardString you need at least DBI 1.611.
StrictlyTyped
See DBI's sql_type_cast utility function.
See "DiscardString" above.
Specifies that when DBI's sql_type_cast function is called on returned data
where a bind type is specified that if the conversion cannot be performed an
error will be raised.
This is probably not a lot of use with DBD::ODBC as if you ask for say an
SQL_INTEGER and the data is not able to be converted to an integer the ODBC
driver will problably return "Invalid character value for cast
specification (SQL-22018)".
NOTE: For DiscardString you need at least DBI 1.611.
TreatAsLOB
See "odbc_lob_read".
Tracing¶
DBD::ODBC now supports the parse_trace_flag and parse_trace_flags methods
introduced in DBI 1.42 (see DBI for a full description). As of DBI 1.604, the
only trace flag defined which is relevant to DBD::ODBC is 'SQL' which
DBD::ODBC supports by outputting the SQL strings (after modification) passed
to the prepare and do methods.
From DBI 1.617 DBI also defines ENC (encoding), CON (connection) TXN
(transaction) and DBD (DBD only) trace flags. DBI's ENC and CON trace flags
are synonomous with DBD::ODBC's odbcunicode and odbcconnection trace flags
though I may remove the DBD::ODBC ones in the future. DBI's DBD trace flag
allows output of only DBD::ODBC trace messages without DBI's trace messages.
Currently DBD::ODBC supports two private trace flags. The 'odbcunicode' flag
traces some unicode operations and the odbcconnection traces the connect
process.
To enable tracing of particular flags you use:
$h->trace($h->parse_trace_flags('SQL|odbcconnection'));
$h->trace($h->parse_trace_flags('1|odbcunicode'));
In the first case 'SQL' and 'odbcconnection' tracing is enabled on $h. In the
second case trace level 1 is set and 'odbcunicode' tracing is enabled.
If you want to enable a DBD::ODBC private trace flag before connecting you need
to do something like:
use DBD::ODBC;
DBI->trace(DBD::ODBC->parse_trace_flag('odbcconnection'));
or
use DBD::ODBC;
DBI->trace(DBD::ODBC->parse_trace_flags('odbcconnection|odbcunicode'));
or
DBI_TRACE=odbcconnection|odbcunicode perl myscript.pl
From DBI 1.617 you can output only DBD::ODBC trace messages using
DBI_TRACE=DBD perl myscript.pl
DBD::ODBC outputs tracing at levels 3 and above (as levels 1 and 2 are reserved
for DBI).
For comprehensive tracing of DBI method calls without all the DBI internals see
DBIx::Log4perl.
Deviations from the DBI specification¶
last_insert_id
DBD::ODBC does not support DBI's last_insert_id. There is no ODBC defined way of
obtaining this information. Generally the mechanism (and it differs vastly
between databases and ODBC drivers) it to issue a select of some form (e.g.,
select @@identity or select sequence.currval from dual, etc).
There are literally dozens of databases and ODBC drivers supported by DBD::ODBC
and I cannot have them all. If you know how to retrieve the information for
last_insert_id and you mail me the ODBC Driver name/version and database
name/version with a small working example I will collect examples and document
them here.
Microsoft Access. Recent versions of MS Access support
select
@@identity to retrieve the last insert ID. See
http://support.microsoft.com/kb/815629. Information provided by Robert
Freimuth.
Comments in SQL
DBI does not say anything in particular about comments in SQL. DBD::ODBC looks
for placeholders in the SQL string and until 1.24_2 it did not recognise
comments in SQL strings so could find what it believes to be a placeholder in
a comment e.g.,
select '1' /* placeholder ? in comment */
select -- named placeholder :named in comment
'1'
I cannot be exact about support for ignoring placeholders in literals but it has
existed for a long time in DBD::ODBC. Support for ignoring placeholders in
comments was added in 1.24_2. If you find a case where a named placeholder is
not ignored and should be, see "odbc_ignore_named_placeholders" for
a workaround and mail me an example along with your ODBC driver name.
do
This is not really a deviation from the DBI specification since DBI allows a
driver to avoid the overhead of creating an DBI statement handle for
do().
DBD::ODBC implements "do" by calling SQLExecDirect in ODBC and not
SQLPrepare followed by SQLExecute so "do" is not the same as:
$dbh->prepare($sql)->execute()
It does this to avoid a round-trip to the server so it is faster. Normally this
is good but some people fall foul of this with MS SQL Server if they call a
procedure which outputs print statements (e.g., backup) as the procedure may
not complete. See the DBD::ODBC FAQ and in general you are better to use
prepare/execute when calling procedures.
In addition, you should realise that since DBD::ODBC does not create a DBI
statement for do calls, if you set up an error handler the handle passed in
when a do fails will be the database handle and not a statement handle.
Mixed placeholder types
There are 3 conventions for place holders in DBI. These are '?', ':N' and
':name' (where 'N' is a number and 'name' is an alpha numeric string not
beginning with a number). DBD::ODBC supports all these methods for naming
placeholders but you must only use one method throughout a particular SQL
string. If you mix placeholder methods you will get an error like:
Can't mix placeholder styles (1/2)
Using the same placeholder more than once
DBD::ODBC does not support (currently) the use of one named placeholder more
than once in the a single SQL string. i.e.,
insert into foo values (:bar, :p1, :p2, :bar);
is not supported because 'bar' is used more than once but:
insert into foo values(:bar, :p1, :p2)
is ok. If you do the former you will get an error like:
DBD::ODBC does not yet support binding a named parameter more than once
Binding named placeholders
Although the DBI documentation (as of 1.604) does not say how named parameters
are bound Tim Bunce has said that in Oracle they are bound with the leading
':' as part of the name and that has always been the case. i.e.,
prepare("insert into mytable values (:fred)");
bind_param(":foo", 1);
DBD::ODBC does not support binding named parameters with the ':' introducer. In
the above example you must use:
bind_param("foo", 1);
In discussion on the dbi-dev list is was suggested that the ':' could be made
optional and there were no basic objections but it has not made it's way into
the pod yet.
Sticky Parameter Types
The DBI specification post 1.608 says in bind_param:
The data type is 'sticky' in that bind values passed to execute()
are bound with the data type specified by earlier bind_param()
calls, if any. Portable applications should not rely on being able
to change the data type after the first C<bind_param> call.
DBD::ODBC does allow a parameter to be rebound with another data type as ODBC
inherently allows this. Therefore you can do:
# parameter 1 set as a SQL_LONGVARCHAR
$sth->bind_param(1, $data, DBI::SQL_LONGVARCHAR);
# without the bind above the $data parameter would be either a DBD::ODBC
# internal default or whatever the ODBC driver said it was but because
# parameter types are sticky, the type is still SQL_LONGVARCHAR.
$sth->execute($data);
# change the bound type to SQL_VARCHAR
# some DBDs will ignore the type in the following, DBD::ODBC does not
$sth->bind_param(1, $data, DBI::SQL_VARCHAR);
disconnect and transactions
DBI does not define whether a driver commits or rolls back any outstanding
transaction when disconnect is called. As such DBD::ODBC cannot deviate from
the specification but you should know it rolls back an uncommitted transaction
when disconnect is called if SQLDisconnect returns state 25000 (transaction in
progress).
execute_for_fetch and execute_array
From version 1.34_1 DBD::ODBC implements its own execute_for_fetch which binds
arrays of parameters and can send multiple rows ("odbc_batch_size")
of parameters through the ODBC driver in one go (this overrides DBI's default
execute_for_fetch). This is much faster when inserting, updating or deleting
many rows in one go. Note, execute_array uses execute_for_fetch when the
parameters are passed for column-wise binding.
However, there are a small number of differences between using DBD::ODBC's
execute_for_fetch compared with using DBI's default implementation (which
simply calls execute repeatedly once per row). The differences you may see
are:
o as DBI's execute_for_fetch does one row at a time the result from execute is
for one row and just about all ODBC drivers can report the number of affected
rows when SQLRowCount is called per execute. When batches of parameters are
sent the driver can still return the number of affected rows but it is usually
per batch rather than per row. As a result, the tuple_status array you may
pass to execute_for_fetch (or execute_array) usually shows -1 (unknown) for
each row although the total affected returned in array context is a correct
total affected.
o not all ODBC drivers have sufficient ODBC support (arguably a bug) for correct
diagnostics support when using arrays. DBI dictates that if a row in the batch
is in error the tuple_status will contain the state, native and error message
text. However the batch may generate multiple errors per row (which DBI says
nothing about) and more than one row may error. In ODBC we get a list of
errors but to associate each one with a particular row we need to call
SQLGetDiagField for SQL_DIAG_ROW_NUMBER and it should say which row in the
batch the diagnostic is associated with. Some ODBC drivers do not support
SQL_DIAG_ROW_NUMBER properly and then DBD::ODBC cannot know which row in the
batch an error refers to. In this case DBD::ODBC will report an error saying
"failed to retrieve diags", state of HY000 and a native of 1 so
you'll still see an error but not necessarily the exact one. Also, when more
than one diagnostic is found for a row DBD::ODBC picks the first one (which is
usually most relevant) as there is no way to report more than one diagnostic
per row in the tuple_status. If the first problem of SQL_DIAG_ROW_NUMBER
proves to be a problem for you the DBD::ODBC tracing will show all errors and
you can also use "odbc_getdiagrec" yourself.
o Binding parameters with execute_array and execute_for_fetch does not allow the
parameter types to be set. However, as parameter types are sticky you can call
bind_param(param_num, undef, {TYPE => sql_type}) before calling
execute_for_fetch/execute_array and the TYPE should be sticky when the batch
of parameters is bound.
o Although you can insert very large columns execute_for_fetch will need
"odbc_batch_size" * max length of parameter per parameter so you may
hit memory limits. If you use DBI's execute_for_fetch DBD::ODBC uses the ODBC
API SQLPutData (see "odbc_putdata_start") which does not require
large amounts of memory as large columns are sent in pieces.
o A lot of drivers have bugs with arrays of parameters (see the ODBC FAQ). e.g.,
as of 18-MAR-2012 I've seen the latest SQLite ODBC driver seg fault and
freeTDS 8/0.91 returns the wrong row count for batches.
o
DO NOT attempt to do an insert/update/delete and a select in the same
SQL with execute_array e.g.,
SET IDENTITY_INSERT mytable ON
insert into mytable (id, name) values (?,?)
SET IDENTITY_INSERT mytable OFF
SELECT SCOPE_IDENTITY()
It just won't/can't work although you may not have noticed when using DBI's
inbuilt execute_* methods. See rt 75687.
type_info_all
Many ODBC drivers now return 20 columns in type_info_all rather than the 19 DBI
documents DBI documents. The 20th column is usually called
"USERTYPE". Recent MS SQL Server ODBC drivers do this. Fortunately
this should not adversely affect you so long as you are using the keys
provided at the start of type_info_all.
Unicode¶
The ODBC specification supports wide character versions (a postfix of 'W') of
some of the normal ODBC APIs e.g., SQLDriverConnectW is a wide character
version of SQLDriverConnect.
In ODBC on Windows the wide characters are defined as SQLWCHARs (2 bytes) and
are UCS-2. On non-Windows, the main driver managers I know of have implemented
the wide character APIs differently:
- unixODBC
- unixODBC mimics the Windows ODBC API precisely meaning the
wide character versions expect and return 2-byte characters in UCS-2.
unixODBC will happily recognise ODBC drivers which only have the ANSI
versions of the ODBC API and those that have the wide versions too.
unixODBC will allow an ANSI application to work with a unicode ODBC driver
and vice versa (although in the latter case you obviously cannot actually
use unicode).
unixODBC does not prevent you sending UTF-8 in the ANSI versions of the ODBC
APIs but whether that is understood by your ODBC driver is another matter.
unixODBC differs in only one way from the Microsoft ODBC driver in terms of
unicode support in that it avoids unnecessary translations between single
byte and double byte characters when an ANSI application is using a
unicode-aware ODBC driver by requiring unicode applications to signal
their intent by calling SQLDriverConnectW first. On Windows, the ODBC
driver manager always uses the wide versions of the ODBC API in ODBC
drivers which provide the wide versions regardless of what the application
really needs and this results in a lot of unnecessary character
translations when you have an ANSI application and a unicode ODBC
driver.
- iODBC
- The wide character versions expect and return wchar_t
types.
DBD::ODBC has gone with unixODBC so you cannot use iODBC with a unicode build of
DBD::ODBC. However, some ODBC drivers support UTF-8 (although how they do this
with SQLGetData reliably I don't know) and so you should be able to use those
with DBD::ODBC not built for unicode.
Enabling and Disabling Unicode support
On Windows Unicode support is enabled by default and to disable it you will need
to specify "-nou" to
Makefile.PL to get back to the original
behavior of DBD::ODBC before any Unicode support was added.
e.g.,
perl Makfile.PL -nou
On non-Windows platforms Unicode support is disabled by default. To enable it
specify "-u" to
Makefile.PL when you configure DBD::ODBC.
e.g.,
perl Makefile.PL -u
Unicode - What is supported?
As of version 1.17 DBD::ODBC has the following unicode support:
- SQL (introduced in 1.16_2)
- Unicode strings in calls to the "prepare" and
"do" methods are supported so long as the
"odbc_execdirect" attribute is not used.
- unicode connection strings (introduced in 1.16_2)
- Unicode connection strings are supported but you will need
a DBI post 1.607 for that.
- column names
- Unicode column names are returned.
- bound columns (introduced in 1.15)
- If the DBMS reports the column as being a wide character
(SQL_Wxxx) it will be bound as a wide character and any returned data will
be converted from UTF-16 to UTF-8 and the UTF-8 flag will then be set on
the data.
- bound parameters
- If the perl scalars you bind to parameters are marked UTF-8
and the DBMS reports the type as being a wide type or you bind the
parameter as a wide type they will be converted to wide characters and
bound as such.
- metadata calls like table_info, column_info
- As of DBD::ODBC 1.32_3 meta data calls accept Unicode
strings.
Since version 1.16_4, the default parameter bind type is SQL_WVARCHAR for
unicode builds of DBD::ODBC. This only affects ODBC drivers which do not
support SQLDescribeParam and only then if you do not specifically set a sql
type on the bind_param method call.
The above Unicode support has been tested with the SQL Server, Oracle 9.2+ and
Postgres drivers on Windows and various Easysoft ODBC drivers on UNIX.
Unicode - What is not supported?
You cannot use unicode parameter names e.g.,
select * from table where column = :unicode_param_name
You cannot use unicode strings in calls to prepare if you set the
odbc_execdirect attribute.
You cannot use the iODBC driver manager with DBD::ODBC built for unicode.
Unicode - Caveats
For Unicode support on any platform in Perl you will need at least Perl 5.8.1 -
sorry but this is the way it is with Perl.
The Unicode support in DBD::ODBC expects a WCHAR to be 2 bytes (as it is on
Windows and as the ODBC specification suggests it is). Until ODBC specifies
any other Unicode support it is not envisioned this will change. On UNIX there
are a few different ODBC driver managers. I have only tested the unixODBC
driver manager (
http://www.unixodbc.org) with Unicode support and it was built
with defaults which set WCHAR as 2 bytes.
I believe that the iODBC driver manager expects wide characters to be wchar_t
types (which are usually 4) and hence DBD::ODBC will not work iODBC when built
for unicode.
The ODBC Driver must expect Unicode data specified in SQLBindParameter and
SQLBindCol to be UTF-16 in local endianness. Similarly, in calls to
SQLPrepareW, SQLDescribeColW and SQLDriverConnectW.
You should be aware that once Unicode support is enabled it affects a number of
DBI methods (some of which you might not expect). For instance, when listing
tables, columns etc some drivers (e.g. Microsoft SQL Server) will report the
column types as wide types even if the strings actually fit in 7-bit ASCII. As
a result, there is an overhead for retrieving this column data as 2 bytes per
character will be transmitted (compared with 1 when Unicode support is not
enabled) and these strings will be converted into UTF-8 but will end up
fitting (in most cases) into 7bit ASCII so a lot of conversion work has been
performed for nothing. If you don't have Unicode table and column names or
Unicode column data in your tables you are best disabling Unicode support.
I am at present unsure if ChopBlanks processing on Unicode strings is working
correctly on UNIX. If nothing else the construct L' ' in dbdimp.c might not
work with all UNIX compilers. Reports of issues and patches welcome.
Unicode implementation in DBD::ODBC
DBD::ODBC uses the wide character versions of the ODBC API and the SQL_WCHAR
ODBC type to support unicode in Perl.
Wide characters returned from the ODBC driver will be converted to UTF-8 and the
perl scalars will have the utf8 flag set (by using sv_utf8_decode).
IMPORTANT
Perl scalars which are UTF-8 and are sent through the ODBC API will be converted
to UTF-16 and passed to the ODBC wide APIs or signalled as SQL_WCHARs (e.g.,
in the case of bound columns). Retrieved data which are wide characters are
converted from UTF-16 to UTF-8. However, you should realise most ODBC drivers
do not support UTF-16, ODBC only talks about wide characters being 2 bytes and
UCS-2 and UCS-2 and UTF-16 are not the same. UCS-2 only supports Unicode
characters in the first plane (the Basic Multilangual Plane or BMP) (code
points U+0000 to U+FFFF), the most frequently used characters. So why does
DBD::ODBC currently encode in UTF-16? For around 97% of Unicode characters in
the range 0-0xFFFF UCS-2 and UTF-16 are exactly the same (and where they
differ there is no valid Unicode character as the range U+D800 to U+DFFF is
reserved from use only as surrogate pairs). As the ODBC API currently uses
UCS-2 it does not support Unicode characters with code points above 0xFFFF (if
you know better I'd like to hear from you). However, because DBD::ODBC uses
UTF-16 encoding you can still insert Unicode characters above 0xFFFF into your
database and retrieve them back correctly but they will not being treated as a
single Unicode character in your database e.g., a "select
length(a_column) from table" with a single Unicode character above 0xFFFF
will most likely return 2 and not 1 so you cannot use database functions on
that data like upper/lower/length etc but you can at least save the data in
your database and get it back. This is a fudge and I cannot say I'm overjoyed
by it but it is what the majority of people who use DBD::ODBC have requested.
When built for unicode, DBD::ODBC will always call SQLDriverConnectW (and not
SQLDriverConnect) even if a) your connection string is not unicode b) you have
not got a DBI later than 1.607, because unixODBC requires SQLDriverConnectW to
be called if you want to call other unicode ODBC APIs later. As a result, if
you build for unicode and pass ASCII strings to the connect method they will
be converted to UTF-16 and passed to SQLDriverConnectW. This should make no
real difference to perl not using unicode connection strings.
You will need a DBI later than 1.607 to support unicode connection strings
because until post 1.607 there was no way for DBI to pass unicode strings to
the DBD.
Unicode and Oracle
You have to set the environment variables "NLS_NCHAR=AL32UTF8" and
"NLS_LANG=AMERICAN_AMERICA.AL32UTF8" (or any other language setting
ending with ".AL32UTF8") before loading DBD::ODBC to make Oracle
return Unicode data. (See also "Oracle and Unicode" in the POD of
DBD::Oracle.)
On Windows, using the Oracle ODBC Driver you have to enable the
Force
SQL_WCHAR support Workaround in the data source configuration to make
Oracle return Unicode to a non-Unicode application. Alternatively, you can
include "FWC=T" in your connect string.
Unless you need to use ODBC, if you want Unicode support with Oracle you are
better off using DBD::Oracle.
Unicode and PostgreSQL
See the odbc_utf8_on parameter to treat all strings as utf8.
Some tests from the original DBD::ODBC 1.13 fail with PostgreSQL 8.0.3, so you
may not want to use DBD::ODBC to connect to PostgreSQL 8.0.3.
Unicode tests fail because PostgreSQL seems not to give any hints about Unicode,
so all data is treated as non-Unicode.
Unless you need to use ODBC, if you want Unicode support with Postgres you are
better off with DBD::Pg as it has a specific attribute named
"pg_enable_utf8" to enable Unicode support.
Unicode and Easysoft ODBC Drivers
We have tested the Easysoft SQL Server, Oracle and ODBC Bridge drivers with
DBD::ODBC built for Unicode. All work as described without modification except
for the Oracle driver you will need to set you NLS_LANG as mentioned above.
Unicode and other ODBC drivers
If you have a unicode-enabled ODBC driver and it works with DBD::ODBC let me
know and I will include it here.
ODBC Support in ODBC Drivers¶
Drivers without SQLDescribeParam
Some drivers do not support the "SQLDescribeParam" ODBC API (e.g.,
Microsoft Access, FreeTDS).
DBD::ODBC uses the "SQLDescribeParam" API when parameters are bound to
your SQL to find the types of the parameters. If the ODBC driver does not
support "SQLDescribeParam", DBD::ODBC assumes the parameters are
"SQL_VARCHAR" or "SQL_WVARCHAR" types (depending on
whether DBD::ODBC is built for unicode or not). In any case, if you bind a
parameter and specify a SQL type this overrides any type DBD::ODBC would
choose.
For ODBC drivers which do not support "SQLDescribeParam" the default
behavior in DBD::ODBC may not be what you want. To change the default
parameter bind type set "odbc_default_bind_type". If, after that you
have some SQL where you need to vary the parameter types used add the SQL type
to the end of the "bind_param" method.
use DBI qw(:sql_types);
$h = DBI->connect;
# set the default bound parameter type
$h->{odbc_default_bind_type} = SQL_VARCHAR;
# bind a parameter with a specific type
$s = $h->prepare(q/insert into mytable values(?)/);
$s->bind_param(1, "\x{263a}", SQL_WVARCHAR);
Version Control¶
DBD::ODBC source code is under version control at svn.perl.org. If you would
like to use the "bleeding" edge version, you can get the latest from
svn.perl.org via Subversion version control. Note there is no guarantee that
this version is any different than what you get from the tarball from CPAN,
but it might be :)
You may read about Subversion at <
http://subversion.tigris.org>
You can get a subversion client from there and check dbd-odbc out via:
svn checkout http://svn.perl.org/modules/dbd-odbc/trunk <your directory name here>
Which will pull all the files from the subversion trunk to your specified
directory. If you want to see what has changed since the last release of
DBD::ODBC read the Changes file or use "svn log" to get a list of
checked in changes.
Contributing¶
There are seven main ways you may help with the development and maintenance of
this module:
- Submitting patches
- Please use Subversion (see above) to get the latest version
of DBD::ODBC from the trunk and submit any patches against that.
Please, before submitting a patch:
svn update
<try and included a test which demonstrates the fix/change working>
<test your patch>
svn diff > describe_my_diffs.patch
and send the resulting file to me and cc the dbi-users@perl.org mailing list
(if you are not a member - why not!).
- Reporting installs
- Install CPAN::Reporter and report you installations. This
is easy to do - see "CPAN Testers Reporting".
- Report bugs
- If you find what you believe is a bug then enter it into
the http://rt.cpan.org/Dist/Display.html?Name=DBD-ODBC
<http://rt.cpan.org/Dist/Display.html?Name=DBD-ODBC> system. Where
possible include code which reproduces the problem including any schema
required and the versions of software you are using.
If you are unsure whether you have found a bug report it anyway or post it
to the dbi-users mailing list.
- pod comments and corrections
- If you find inaccuracies in the DBD::ODBC pod or have a
comment which you think should be added then go to
<http://annocpan.org> and submit them there. I get an email for
every comment added and will review each one and apply any changes to the
documentation.
- Review DBD::ODBC
- Add your review of DBD::ODBC on
<http://cpanratings.perl.org>.
If you are a member on ohloh then add your review or register your use of
DBD::ODBC at <http://www.ohloh.net/projects/perl_dbd_odbc>.
- submit test cases
- Most DBDs are built against a single client library for the
database.
Unlike other DBDs, DBD::ODBC works with many different ODBC drivers.
Although they all should be written with regard to the ODBC specification
drivers have bugs and in some places the specification is open to
interpretation. As a result, when changes are applied to DBD::ODBC it is
very easy to break something in one ODBC driver.
What helps enormously to identify problems in the many combinations of
DBD::ODBC and ODBC drivers is a large test suite. I would greatly
appreciate any test cases and in particular any new test cases for
databases other than MS SQL Server.
- Test DBD::ODBC
- I have a lot of problems deciding when to move a
development release to an official release since I get few test reports
for development releases. What often happens is I call for testers on
various lists, get a few and then get inundated with requests to do an
official release. Then I do an official release and loads of rts appear
out of nowhere and the cycle starts again.
DBD::ODBC by its very nature works with many ODBC Drivers and it is
impossible for me to have and test them all (this differs from other
DBDs). If you depend on DBD::ODBC you should be interested in new releases
and if you send me your email address suggesting you are prepared to be
part of the DBD::ODBC testing network I will credit you in the Changes
file and perhaps the main DBD::ODBC file.
CPAN Testers Reporting¶
Please, please, please (is that enough), consider installing CPAN::Reporter so
that when you install perl modules a report of the installation success or
failure can be sent to cpan testers. In this way module authors 1) get
feedback on the fact that a module is being installed 2) get to know if there
are any installation problems. Also other people like you may look at the test
reports to see how successful they are before choosing the version of a module
to install.
See this guide on how to get started with sending test reports:
<
http://wiki.cpantesters.org/wiki/QuickStart>.
Others/todo?¶
Level 2
SQLColumnPrivileges
SQLProcedureColumns
SQLProcedures
SQLTablePrivileges
SQLDrivers
SQLNativeSql
Random Links¶
These are in need of sorting and annotating. Some are relevant only to ODBC
developers.
You can find DBD::ODBC on ohloh now at:
<
http://www.ohloh.net/projects/perl_dbd_odbc>
If you use ohloh and DBD::ODBC please say you use it and rate it.
There is a good search engine for the various Perl DBI lists at the following
URLS:
http://perl.markmail.org/search/list:org.perl.dbi-users
<
http://perl.markmail.org/search/list:org.perl.dbi-users>
http://perl.markmail.org/search/list:org.perl.dbi-dev
<
http://perl.markmail.org/search/list:org.perl.dbi-dev>
http://perl.markmail.org/search/list:org.perl.dbi-announce
<
http://perl.markmail.org/search/list:org.perl.dbi-announce>
<
http://www.syware.com>
<
http://www.microsoft.com/odbc>
For Linux/Unix folks, compatible ODBC driver managers can be found at:
<
http://www.unixodbc.org> (unixODBC source and rpms)
<
http://www.iodbc.org> (iODBC driver manager source)
For Linux/Unix folks, you can checkout the following for ODBC Drivers and
Bridges:
<
http://www.easysoft.com>
<
http://www.openlinksw.com>
<
http://www.datadirect.com>
<
http://www.atinet.com>
Some useful tutorials:¶
Debugging Perl DBI:
http://www.easysoft.com/developer/languages/perl/dbi-debugging.html
<
http://www.easysoft.com/developer/languages/perl/dbi-debugging.html>
Enabling ODBC support in Perl with Perl DBI and DBD::ODBC:
<
http://www.easysoft.com/developer/languages/perl/dbi_dbd_odbc.html>
Perl DBI/DBD::ODBC Tutorial Part 1 - Drivers, Data Sources and Connection:
<
http://www.easysoft.com/developer/languages/perl/dbd_odbc_tutorial_part_1.html>
Perl DBI/DBD::ODBC Tutorial Part 2 - Introduction to retrieving data from your
database:
<
http://www.easysoft.com/developer/languages/perl/dbd_odbc_tutorial_part_2.html>
Perl DBI/DBD::ODBC Tutorial Part 3 - Connecting Perl on UNIX or Linux to
Microsoft SQL Server:
<
http://www.easysoft.com/developer/languages/perl/sql_server_unix_tutorial.html>
Perl DBI - Put Your Data On The Web:
<
http://www.easysoft.com/developer/languages/perl/tutorial_data_web.html>
Multiple Active Statements (MAS) and DBD::ODBC
http://www.easysoft.com/developer/languages/perl/multiple-active-statements.html
<
http://www.easysoft.com/developer/languages/perl/multiple-active-statements.html>
64-bit ODBC
http://www.easysoft.com/developer/interfaces/odbc/64-bit.html
<
http://www.easysoft.com/developer/interfaces/odbc/64-bit.html>
Frequently Asked Questions¶
Frequently asked questions are now in DBD::ODBC::FAQ. Run "perldoc
DBD::ODBC::FAQ" to view them.
CONFIGURATION AND ENVIRONMENT¶
You should consult the documentation for the ODBC Driver Manager you are using.
DEPENDENCIES¶
DBI
Test::Simple
INCOMPATIBILITIES¶
None known.
BUGS AND LIMITATIONS¶
None known other than the deviations from the DBI specification mentioned above
in "Deviations from the DBI specification".
Please report any to me via the CPAN RT system. See <
http://rt.cpan.org/>
for more details.
AUTHOR¶
Tim Bunce
Jeff Urlwin
Thomas K. Wenrich
Martin J. Evans
LICENSE AND COPYRIGHT¶
This program is free software; you can redistribute it and/or modify it under
the same terms as Perl itself. See perlartistic. This program is distributed
in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the
implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
Portions of this software are Copyright Tim Bunce, Thomas K. Wenrich, Jeff
Urlwin and Martin J. Evans - see the source.
SEE ALSO¶
DBI