Check if NULL exists in Postgres array

Question

Similar to this question, how can I find if a NULL value exists in an array?

Here are some attempts.

SELECT num, ar, expected,
  ar @> ARRAY[NULL]         


        

Answer 1

PostgreSQL 9.5 (I know you spcified 9.1, but anyway) has the array_position() function to do just what you want without having to use the horribly inefficient unnest() for something as trivial as this (see test4):

patrick@puny:~$ psql -d test
psql (9.5.0)
Type "help" for help.

test=# SELECT num, ar, expected,
  ar @> ARRAY[NULL]::int[] AS test1,
  NULL = ANY (ar) AS test2,
  array_to_string(ar, ', ') <> array_to_string(ar, ', ', '(null)') AS test3,
  coalesce(array_position(ar, NULL::int), 0) > 0 AS test4
FROM (
  SELECT 1 AS num, '{1,2,NULL}'::int[] AS ar, true AS expected
  UNION SELECT 2, '{1,2,3}'::int[], false
) td ORDER BY num;
 num |     ar     | expected | test1 | test2 | test3 | test4
-----+------------+----------+-------+-------+-------+-------
   1 | {1,2,NULL} | t        | f     |       | t     | t
   2 | {1,2,3}    | f        | f     |       | f     | f
(2 rows)