Adding a unique constraint on a nullable column in PSQL

Question

I am having a table with two columns. Want to add unique constraint on both columns. One of the column is nullable.

I m trying with this syntax:

ALTER TABLE a ADD CONSTRAINT a_unq UNIQUE (a_id, (coalesce(a_name, '')));

Its prompting error at or near "("

Answer 1

You don't need to use coalesce in that case. Just create constraint in the usual way:

ALTER TABLE a ADD CONSTRAINT a_unq UNIQUE (a_id, a_name);

Answer 2

If you uactually need the solution was in PostgreSQL multiple nullable columns in unique constraint : just create UNIQUE index on table, it will stop inserts even if it isn't a constraint declared in table definition:

CREATE UNIQUE INDEX ex_12345 ON example
        (coalesce(FIELD1, -1)
        , coalesce(FIELD2, -1)
        , coalesce(FIELD3, -1)
        , coalesce(FIELD4, -1)
        , coalesce(FIELD5, -1)
        )
        ;