![]() ![]() The easiest way to turn these commands into proper scripts is to just use the psql output feature: ORDER BY CASE WHEN contype='f' THEN 0 ELSE 1 END DESC,contype DESC,nspname DESC,relname DESC,conname DESC Īgain, note the reversed order that is necessary so we create PRIMARY KEYs and UNIQUE constraints before we create the FOREIGN KEYs. Pg_get_constraintdef(pg_constraint.oid)||' ' To generate a script to reload the constraints: Note that the order is important - we must drop FOREIGN KEYs before we drop PRIMARY KEYs and UNIQUE constraints, since they depend on each other. ORDER BY CASE WHEN contype='f' THEN 0 ELSE 1 END,contype,nspname,relname,conname INNER JOIN pg_namespace ON pg_namespace.oid=pg_class.relnamespace INNER JOIN pg_class ON conrelid=pg_class.oid To generate a script to drop constraints: Adding filters for just a single table/namespace/constrainttype is trivial, but left as an exercise for the reader. The following simple queries will generate SQL scripts that drop all your constraints, and then re-create them. All of them, or maybe just the FOREIGN KEYs, depending on exactly what you are doing. Of the kind where you load or update lots of data - which means that it will run a lot faster with the constraints in the database turned off. The idea is: you have some large operations you are doing on your database. This blog post presented a step-by-step guide for dropping a unique constraint in Postgres.I do this fairly often, but after talking to some other people I realized it might be a good idea to share a couple of quick SQL scripts. 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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