On 205h of July Andrew Dunstan committed patch by Andres Freund :
Log Message: ----------- DROP IF EXISTS for columns and constraints. Andres Freund.
The functionality is self-explanatory, so let's just show some usage examples:
Test table:
# create table test (a int4, b int4); CREATE TABLE
Drop non-existing column old way:
# alter table test drop column c; ERROR: column "c" of relation "test" does not exist
and new way:
# alter table test drop column if exists c; NOTICE: column "c" of relation "test" does not exist, skipping ALTER TABLE
Now, for constraints:
# alter table test add primary key (a); NOTICE: ALTER TABLE / ADD PRIMARY KEY will create implicit index "test_pkey" for table "test" ALTER TABLE
New way of removal:
# alter table test drop constraint typo_pkey; ERROR: constraint "typo_pkey" of relation "test" does not exist
New way:
# alter table test drop constraint if exists typo_pkey; NOTICE: constraint "typo_pkey" of relation "test" does not exist, skipping ALTER TABLE
With these additions now all objects can be dropped in “if exists" way (as far as I know).
Now, if we'd only get “CREATE UNLESS EXISTS" (and CREATE OR REPLACE for all object types) I would be soooo happy.