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|CREATE STATISTICS(7)||PostgreSQL 11.9 Documentation||CREATE STATISTICS(7)|
NAME¶CREATE_STATISTICS - define extended statistics
CREATE STATISTICS [ IF NOT EXISTS ] statistics_name [ ( statistics_kind [, ... ] ) ] ON column_name, column_name [, ...] FROM table_name
DESCRIPTION¶CREATE STATISTICS will create a new extended statistics object tracking data about the specified table, foreign table or materialized view. The statistics object will be created in the current database and will be owned by the user issuing the command.
If a schema name is given (for example, CREATE STATISTICS myschema.mystat ...) then the statistics object is created in the specified schema. Otherwise it is created in the current schema. The name of the statistics object must be distinct from the name of any other statistics object in the same schema.
PARAMETERS¶IF NOT EXISTS
NOTES¶You must be the owner of a table to create a statistics object reading it. Once created, however, the ownership of the statistics object is independent of the underlying table(s).
EXAMPLES¶Create table t1 with two functionally dependent columns, i.e. knowledge of a value in the first column is sufficient for determining the value in the other column. Then functional dependency statistics are built on those columns:
CREATE TABLE t1 ( a int, b int ); INSERT INTO t1 SELECT i/100, i/500 FROM generate_series(1,1000000) s(i); ANALYZE t1; -- the number of matching rows will be drastically underestimated: EXPLAIN ANALYZE SELECT * FROM t1 WHERE (a = 1) AND (b = 0); CREATE STATISTICS s1 (dependencies) ON a, b FROM t1; ANALYZE t1; -- now the row count estimate is more accurate: EXPLAIN ANALYZE SELECT * FROM t1 WHERE (a = 1) AND (b = 0);
Without functional-dependency statistics, the planner would assume that the two WHERE conditions are independent, and would multiply their selectivities together to arrive at a much-too-small row count estimate. With such statistics, the planner recognizes that the WHERE conditions are redundant and does not underestimate the row count.
COMPATIBILITY¶There is no CREATE STATISTICS command in the SQL standard.
SEE ALSO¶ALTER STATISTICS (ALTER_STATISTICS(7)), DROP STATISTICS (DROP_STATISTICS(7))