![]() 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. 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. 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). 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. 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 Refer to CREATE TABLE for a further description of valid parameters.ALTER TABLE name The space is reclaimed over time as existing rows are updated.Ĭhanging any part of a system catalog table isn't permitted. Thus, dropping a column is quick, but it doesn't immediately reduce the on-disk size of your table since the space occupied by the dropped column isn't reclaimed. Subsequent insert and update operations in the table store a null value for the column. The DROP COLUMN form doesn't physically remove the column but makes it invisible to SQL operations. Adding a CHECK or NOT NULL constraint requires scanning the table to verify that existing rows meet the constraint. This can take a long time for a large table, and it temporarily requires double the disk space. Adding a column with a non-null default requires rewriting the entire table. When you invoke ADD COLUMN, all existing rows in the table are initialized with the column’s default value (null if no DEFAULT clause is specified). The integer indicates the degree of parallelism, which is the number of parallel_workers used in the parallel operation to perform a parallel scan on a table. Specify NOPARALLEL to reset parallelism to default values. If you specify PARALLEL without including a degree of parallelism, the index uses default parallelism. You can also specify the degree of parallelism by setting the parallel_workers parameter when performing a parallel scan on a table. Specify PARALLEL to select a degree of parallelism. The name (possibly schema-qualified) of an existing table to alter.Īutomatically drop objects that depend on the dropped constraint. You must own the table to use ALTER TABLE. ON AUTHORIZATION command to alter a trigger's implicit object owner. However, when the ownership of a table is changed, the ownership of the trigger's implicit objects is updated when they're matched with a table owner owning a trigger. reloptions shows the parallel_workers parameter as 0.Ī superuser has permission to create a trigger on any user's table, but a user can create a trigger only on the table they own. The NOPARALLEL clause resets the values to their defaults. The PARALLEL clause sets the degree of parallelism for a table. The RENAME forms change the name of a table (or an index, sequence, or view) or the name of a column in a table. ![]() Currently, constraints on tables don't need unique names, so there might be more than one constraint matching the specified name. Indexes and table constraints involving the column are dropped as well. This form adds a column to the table using the same syntax as CREATE TABLE. Toggle Wrap Copy ADD ] DROP COLUMN ADD DROP CONSTRAINT DescriptionĪLTER TABLE changes the definition of an existing table.
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