Hello, I have a sample table describe as follows, anyone knows how to checking the existence of a constraint?
oviddb=# \d myTable Column | Type | Modifiers ---------+----------+----------- orderid | smallint | not null modelid | smallint | not null Indexes: "mytable_orderid_key" UNIQUE, btree (orderid) For example, how to know that myTable has a constraint with name "mytable_orderid_key"? I have this problem because when doing migration script, some old table may have this constraint or may not have. And after migration, we want to add this constraint: If I just run the command: alter table myTable add Unique (orderid) in the migration script, when the constraint exits, a new index will be created as "mytable_orderid_key1" UNIQUE, btree (orderid) So, it causes some duplication. oviddb=# \d myTable Column | Type | Modifiers ---------+----------+----------- orderid | smallint | not null modelid | smallint | not null Indexes: "mytable_orderid_key" UNIQUE, btree (orderid) "mytable_orderid_key1" UNIQUE, btree (orderid) My question becomes how to write sql statement with following semantecs if constraint unique (orderid) exists do nothing else alter table myTable add Unique (orderid) Thank you so much! -- View this message in context: http://postgresql.1045698.n5.nabble.com/How-to-checking-the-existance-of-constraints-for-a-table-tp3368417p3368417.html Sent from the PostgreSQL - sql mailing list archive at Nabble.com. -- Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-sql