NAME¶
DBD::SQLite2 - Self Contained RDBMS in a DBI Driver (sqlite 2.x)
SYNOPSIS¶
use DBI;
my $dbh = DBI->connect("dbi:SQLite2:dbname=dbfile","","");
DESCRIPTION¶
SQLite is a public domain RDBMS database engine that you can find at
http://www.sqlite.org/.
Rather than ask you to install SQLite first, because SQLite is public domain,
DBD::SQLite2 includes the entire thing in the distribution. So in order to get
a fast transaction capable RDBMS working for your perl project you simply have
to install this module, and
nothing else.
For real work please use the updated DBD::SQLite driver with the up-to-date
sqlite3 backend. SQLite2 supports the following features:
- Implements a large subset of SQL92
- See http://www.sqlite.org/lang.html for details.
- A complete DB in a single disk file
- Everything for your database is stored in a single disk file, making it
easier to move things around than with DBD::CSV.
- Atomic commit and rollback
- Yes, DBD::SQLite2 is small and light, but it supports full
transactions
- Extensible
- User-defined aggregate or regular functions can be registered with the SQL
parser.
There's lots more to it, so please refer to the docs on the SQLite web page,
listed above, for SQL details. Also refer to DBI for details on how to use DBI
itself.
The API works like every DBI module does. Please see DBI for more details about
core features.
Currently many statement attributes are not implemented or are limited by the
typeless nature of the SQLite2 database.
DRIVER PRIVATE ATTRIBUTES¶
Database Handle Attributes¶
- sqlite_version
- Returns the version of the SQLite library which DBD::SQLite2 is using,
i.e, "2.8.15".
- sqlite_encoding
- Returns either "UTF-8" or "iso8859" to indicate how
the SQLite library was compiled.
- sqlite_handle_binary_nulls
- Set this attribute to 1 to transparently handle binary nulls in quoted and
returned data.
NOTE: This will cause all backslash characters ("\") to be
doubled up in all columns regardless of whether or not they contain binary
data or not. This may break your database if you use it from another
application. This does not use the built in
"sqlite_encode_binary" and "sqlite_decode_binary"
functions, which may be considered a bug.
DRIVER PRIVATE METHODS¶
$dbh->func('last_insert_rowid')¶
This method returns the last inserted rowid. If you specify an INTEGER PRIMARY
KEY as the first column in your table, that is the column that is returned.
Otherwise, it is the hidden ROWID column. See the sqlite docs for details.
$dbh->func( $name, $argc, $func_ref, "create_function" )¶
This method will register a new function which will be useable in SQL query. The
method's parameters are:
- $name
- The name of the function. This is the name of the function as it will be
used from SQL.
- $argc
- The number of arguments taken by the function. If this number is -1, the
function can take any number of arguments.
- $func_ref
- This should be a reference to the function's implementation.
For example, here is how to define a
now() function which returns the
current number of seconds since the epoch:
$dbh->func( 'now', 0, sub { return time }, 'create_function' );
After this, it could be use from SQL as:
INSERT INTO mytable ( now() );
$dbh->func( $name, $argc, $pkg, 'create_aggregate' )¶
This method will register a new aggregate function which can then used from SQL.
The method's parameters are:
- $name
- The name of the aggregate function, this is the name under which the
function will be available from SQL.
- $argc
- This is an integer which tells the SQL parser how many arguments the
function takes. If that number is -1, the function can take any number of
arguments.
- $pkg
- This is the package which implements the aggregator interface.
The aggregator interface consists of defining three methods:
- new()
- This method will be called once to create an object which should be used
to aggregate the rows in a particular group. The step() and
finalize() methods will be called upon the reference return by the
method.
- step(@_)
- This method will be called once for each rows in the aggregate.
- finalize()
- This method will be called once all rows in the aggregate were processed
and it should return the aggregate function's result. When there is no
rows in the aggregate, finalize() will be called right after
new().
Here is a simple aggregate function which returns the variance (example adapted
from pysqlite):
package variance;
sub new { bless [], shift; }
sub step {
my ( $self, $value ) = @_;
push @$self, $value;
}
sub finalize {
my $self = $_[0];
my $n = @$self;
# Variance is NULL unless there is more than one row
return undef unless $n || $n == 1;
my $mu = 0;
foreach my $v ( @$self ) {
$mu += $v;
}
$mu /= $n;
my $sigma = 0;
foreach my $v ( @$self ) {
$sigma += ($x - $mu)**2;
}
$sigma = $sigma / ($n - 1);
return $sigma;
}
$dbh->func( "variance", 1, 'variance', "create_aggregate" );
The aggregate function can then be used as:
SELECT group_name, variance(score) FROM results
GROUP BY group_name;
NOTES¶
To access the database from the command line, try using dbish which comes with
the DBI module. Just type:
dbish dbi:SQLite:foo.db
On the command line to access the file
foo.db.
Alternatively you can install SQLite from the link above without conflicting
with DBD::SQLite2 and use the supplied "sqlite" command line tool.
SQLite is fast, very fast. I recently processed my 72MB log file with it,
inserting the data (400,000+ rows) by using transactions and only committing
every 1000 rows (otherwise the insertion is quite slow), and then performing
queries on the data.
Queries like count(*) and avg(bytes) took fractions of a second to return, but
what surprised me most of all was:
SELECT url, count(*) as count FROM access_log
GROUP BY url
ORDER BY count desc
LIMIT 20
To discover the top 20 hit URLs on the site (
http://axkit.org), and it returned
within 2 seconds. I'm seriously considering switching my log analysis code to
use this little speed demon!
Oh yeah, and that was with no indexes on the table, on a 400MHz PIII.
For best performance be sure to tune your hdparm settings if you are using
linux. Also you might want to set:
PRAGMA default_synchronous = OFF
Which will prevent sqlite from doing fsync's when writing (which slows down
non-transactional writes significantly) at the expense of some peace of mind.
Also try playing with the cache_size pragma.
BUGS¶
Likely to be many, please use
http://rt.cpan.org/ for reporting bugs.
AUTHOR¶
Matt Sergeant, matt@sergeant.org
Perl extension functions contributed by Francis J. Lacoste
<flacoste@logreport.org> and Wolfgang Sourdeau
<wolfgang@logreport.org>. Maintenance help by Reini Urban
<rurban@cpan.org>
SEE ALSO¶
DBD::SQLite, DBI.