For example, a value of -1 implies that all values in the column are distinct, while a value of -0.5 implies that each value appears twice on the average. When set to a negative value, which must be greater than or equal to -1, ANALYZE will assume that the number of distinct nonnull values in the column is linear in the size of the table the exact count is to be computed by multiplying the estimated table size by the absolute value of the given number. When set to a positive value, ANALYZE will assume that the column contains exactly the specified number of distinct nonnull values.
#ALTER TABLE ADD FOREIGN KEY POSTGRES PLUS#
n_distinct affects the statistics for the table itself, while n_distinct_inherited affects the statistics gathered for the table plus its inheritance children.
Currently, the only defined per-attribute options are n_distinct and n_distinct_inherited, which override the number-of-distinct-values estimates made by subsequent ANALYZE operations. This form sets or resets per-attribute options.
#ALTER TABLE ADD FOREIGN KEY POSTGRES UPDATE#
SET STATISTICS acquires a SHARE UPDATE EXCLUSIVE lock. For more information on the use of statistics by the PostgreSQL query planner, refer to Section 14.2. With the below table structure, we can see three FOREIGN KEY constraints. Verify new keys are in place and updated. Use ALTER TABLE command to add the needed FOREIGN KEY ‘s back to the table. Use ALTER TABLE command to drop any existing FOREIGN KEY ‘s. The target can be set in the range 0 to 10000 alternatively, set it to -1 to revert to using the system default statistics target ( default_statistics_target). We will follow this order to update the FOREIGN KEY ‘s. This form sets the per-column statistics-gathering target for subsequent ANALYZE operations.
sequence_option is an option supported by ALTER SEQUENCE such as INCREMENT BY. These forms alter the sequence that underlies an existing identity column. If DROP IDENTITY IF EXISTS is specified and the column is not an identity column, no error is thrown.
Like SET DEFAULT, these forms only affect the behavior of subsequent INSERT and UPDATE commands they do not cause rows already in the table to change. These forms change whether a column is an identity column or change the generation attribute of an existing identity column. RENAME CONSTRAINT constraint_name TO new_constraint_nameĪLTER TABLE ALL IN TABLESPACE name ]ĪTTACH PARTITION partition_name AS IDENTITY
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