DO $$
BEGIN
  IF NOT EXISTS (
    SELECT 1 FROM information_schema.table_constraints
    WHERE table_schema = '{{.SchemaName}}'
      AND table_name = '{{.TableName}}'
      AND constraint_name = '{{.ConstraintName}}'
  ) THEN
    ALTER TABLE {{.SchemaName}}.{{.TableName}}
      ADD CONSTRAINT {{.ConstraintName}} PRIMARY KEY ({{.Columns}});
  END IF;
END;
$$;