CASCADEĪutomatically drop objects that depend on the index, and in turn all objects that depend on those objects (see Section 5.14). The name (optionally schema-qualified) of an index to remove. IF EXISTSĭo not throw an error if the index does not exist. Lastly, indexes on partitioned tables cannot be dropped using this option.įor temporary tables, DROP INDEX is always non-concurrent, as no other session can access them, and non-concurrent index drop is cheaper. (Thus, an index that supports a UNIQUE or PRIMARY KEY constraint cannot be dropped this way.) Also, regular DROP INDEX commands can be performed within a transaction block, but DROP INDEX CONCURRENTLY cannot. Only one index name can be specified, and the CASCADE option is not supported. There are several caveats to be aware of when using this option. With this option, the command instead waits until conflicting transactions have completed. A normal DROP INDEX acquires an ACCESS EXCLUSIVE lock on the table, blocking other accesses until the index drop can be completed. This blog post presented a step-by-step guide for dropping a unique constraint in Postgres.Drop the index without locking out concurrent selects, inserts, updates, and deletes on the index's table. UNIQUE constraints can be dropped by running the ALTER TABLE command with the " DROP CONSTRAINT" clause followed by the constraint’s name. The output clearly shows that the unique constraint has been successfully dropped from the “college” table.Įxecute the “DROP CONSTRAINT” with the collaboration of the “ ALTER TABLE” statement to drop a specific constraint from a table. To verify the working of the DROP CONSTRAINT, let’s execute the command mentioned below: \d college The constraint “ running” in the existing table “ college” has been dropped, which can be verified through the “ ALTER TABLE” message. For instance, the statement is given below: ALTER TABLE college The “ALTER TABLE” statement is utilized with the “DROP CONSTRAINT” clause to drop the constraint. Step 3: DROP UNIQUE CONSTRAINT in PostgreSQL The output shows that the UNIQUE constraint has been added to the selected table. After table alteration, the modified table’s structure will be as follows: \d college The "ALTER TABLE" message in the output confirms that the unique constraint has been added to the table. For this purpose, the statement is as follows: ALTER TABLE collegeĪDD CONSTRAINT running UNIQUE (teach_id) For this purpose, write the “ ADD CONSTRAINT” clause with a UNIQUE constraint and specify the constraint's name, such as “ running”. In any existing table, such as “college”, a unique constraint can be added using the “ ALTER TABLE” statement. Step 2: ADD UNIQUE CONSTRAINT in PostgreSQL The “ CREATE TABLE” message verifies that the “ college” table has been successfully created. Add columns such as std_id, teach_id, sport_date, and notes in this table: CREATE TABLE college( To drop unique constraints from a table, users must follow the syntax stated below: ALTER TABLE tbl_nameĭROP CONSTRAINT constraint_name UNIQUE (col_name) ĪLTER TABLE is a command in Postgres used to alter/modify a table, while “ DROP CONSTRAINT” is a clause that drops the existing unique constraint from the table.įirst, create a " college " table with the “ CREATE TABLE” statement. In the PostgreSQL database, the “ DROP CONSTRAINT” clause removes the rule or policy that is already set using the “ ADD CONSTRAINT” clause. How to DROP UNIQUE CONSTRAINT in PostgreSQL?
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