milicorps.blogg.se

1. #Postgresql alter table add constraint unique update#
2. #Postgresql alter table add constraint unique plus#

When adding a UNIQUE index on a column (or a set of columns) which have duplicated values, an error will be produced and the statement will be stopped. This is also true for non-transactional tables. If another connection is using the table, a metadata lock is active, and this statement will wait until the lock is released. You can also change the comment for the table and the storage engine of the | EXCHANGE PARTITION partition_name WITH TABLE tbl_nameĪLTER TABLE enables you to change the structure of an existing table.įor example, you can add or delete columns, create or destroy indexes,Ĭhange the type of existing columns, or rename columns or the table | partition_options | CONVERT TABLE normal_table TO partition_definition | CONVERT PARTITION partition_name TO TABLE tbl_name EXTENDED is the default for most data types that support non- PLAIN storage.ALTER TABLE tbl_nameĪlter_specification. EXTERNAL is for external, uncompressed data, and EXTENDED is for external, compressed data. PLAIN must be used for fixed-length values such as integer and is inline, uncompressed. This controls whether this column is held inline or in a secondary TOAST table, and whether the data should be compressed or not. This form sets the storage mode for a column.

#Postgresql alter table add constraint unique update#

For more information on the use of statistics by the Postgres Pro query planner, refer to Section 14.2.Ĭhanging per-attribute options acquires a SHARE UPDATE EXCLUSIVE lock. Specify a value of 0 to revert to estimating the number of distinct values normally. This can be useful when the size of the table changes over time, since the multiplication by the number of rows in the table is not performed until query planning time.

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.

#Postgresql alter table add constraint unique 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. SET STATISTICS acquires a SHARE UPDATE EXCLUSIVE lock. For more information on the use of statistics by the Postgres Pro 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