[PostgreSQL: create constraint if not exists] not sure of sql compatibility with other engines #postgres #constraint #sql

create_constraint_if_not_exists.sql

// vim: syntax=sql

CREATE OR REPLACE FUNCTION create_constraint_if_not_exists (t_name text, c_name text, constraint_sql text)
  RETURNS void
AS
$BODY$
  BEGIN
    -- Look for our constraint
    IF NOT EXISTS (SELECT constraint_name
                   FROM information_schema.constraint_column_usage
                   WHERE constraint_name = c_name) THEN
        EXECUTE 'ALTER TABLE ' || t_name || ' ADD CONSTRAINT ' || c_name || ' ' || constraint_sql;
    END IF;
  END;
$BODY$
LANGUAGE plpgsql VOLATILE;

SELECT create_constraint_if_not_exists('foo', 'bar', 'CHECK (foobies < 100);');