Check if NULL exists in Postgres array - sql

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]::int[] AS test1,
NULL = ANY (ar) AS test2,
array_to_string(ar, ', ') <> array_to_string(ar, ', ', '(null)') AS test3
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
-----+------------+----------+-------+-------+-------
1 | {1,2,NULL} | t | f | | t
2 | {1,2,3} | f | f | | f
(2 rows)
Only a trick with array_to_string shows the expected value. Is there a better way to test this?

Answer 1

Postgres 9.5 or later
Or use array_position(). Basically:
SELECT array_position(arr, NULL) IS NOT NULL AS array_has_null
See demo below.
Postgres 9.3 or later
You can test with the built-in functions array_remove() or array_replace().
Postgres 9.1 or any version
If you know a single element that can never exist in your arrays, you can use this fast expression. Say, you have an array of positive numbers, and -1 can never be in it:
-1 = ANY(arr) IS NULL
Related answer with detailed explanation:
Is array all NULLs in PostgreSQL
If you cannot be absolutely sure, you could fall back to one of the expensive but safe methods with unnest(). Like:
(SELECT bool_or(x IS NULL) FROM unnest(arr) x)
or:
EXISTS (SELECT 1 FROM unnest(arr) x WHERE x IS NULL)
But you can have fast and safe with a CASE expression. Use an unlikely number and fall back to the safe method if it should exist. You may want to treat the case arr IS NULL separately. See demo below.
Demo
SELECT num, arr, expect
, -1 = ANY(arr) IS NULL AS t_1 -- 50 ms
, (SELECT bool_or(x IS NULL) FROM unnest(arr) x) AS t_2 -- 754 ms
, EXISTS (SELECT 1 FROM unnest(arr) x WHERE x IS NULL) AS t_3 -- 521 ms
, CASE -1 = ANY(arr)
WHEN FALSE THEN FALSE
WHEN TRUE THEN EXISTS (SELECT 1 FROM unnest(arr) x WHERE x IS NULL)
ELSE NULLIF(arr IS NOT NULL, FALSE) -- catch arr IS NULL -- 55 ms
-- ELSE TRUE -- simpler for columns defined NOT NULL -- 51 ms
END AS t_91
, array_replace(arr, NULL, 0) <> arr AS t_93a -- 99 ms
, array_remove(arr, NULL) <> arr AS t_93b -- 96 ms
, cardinality(array_remove(arr, NULL)) <> cardinality(arr) AS t_94 -- 81 ms
, COALESCE(array_position(arr, NULL::int), 0) > 0 AS t_95a -- 49 ms
, array_position(arr, NULL) IS NOT NULL AS t_95b -- 45 ms
, CASE WHEN arr IS NOT NULL
THEN array_position(arr, NULL) IS NOT NULL END AS t_95c -- 48 ms
FROM (
VALUES (1, '{1,2,NULL}'::int[], true) -- extended test case
, (2, '{-1,NULL,2}' , true)
, (3, '{NULL}' , true)
, (4, '{1,2,3}' , false)
, (5, '{-1,2,3}' , false)
, (6, NULL , null)
) t(num, arr, expect);
Result:
num | arr | expect | t_1 | t_2 | t_3 | t_91 | t_93a | t_93b | t_94 | t_95a | t_95b | t_95c
-----+-------------+--------+--------+------+-----+------+-------+-------+------+-------+-------+-------
1 | {1,2,NULL} | t | t | t | t | t | t | t | t | t | t | t
2 | {-1,NULL,2} | t | f --!! | t | t | t | t | t | t | t | t | t
3 | {NULL} | t | t | t | t | t | t | t | t | t | t | t
4 | {1,2,3} | f | f | f | f | f | f | f | f | f | f | f
5 | {-1,2,3} | f | f | f | f | f | f | f | f | f | f | f
6 | NULL | NULL | t --!! | NULL | f | NULL | NULL | NULL | NULL | f | f | NULL
Note that array_remove() and array_position() are not allowed for multi-dimensional arrays. All expressions to the right of t_93a only work for 1-dimenstioal arrays.
db<>fiddle here - Postgres 13, with more tests
Old sqlfiddle
Benchmark setup
The added times are from a benchmark test with 200k rows in Postgres 9.5. This is my setup:
CREATE TABLE t AS
SELECT row_number() OVER() AS num
, array_agg(elem) AS arr
, bool_or(elem IS NULL) AS expected
FROM (
SELECT CASE WHEN random() > .95 THEN NULL ELSE g END AS elem -- 5% NULL VALUES
, count(*) FILTER (WHERE random() > .8)
OVER (ORDER BY g) AS grp -- avg 5 element per array
FROM generate_series (1, 1000000) g -- increase for big test case
) sub
GROUP BY grp;
Function wrapper
For repeated use, I would create a function in Postgres 9.5 like this:
CREATE OR REPLACE FUNCTION f_array_has_null (anyarray)
RETURNS bool
LANGUAGE sql IMMUTABLE PARALLEL SAFE AS
'SELECT array_position($1, NULL) IS NOT NULL';
PARALLEL SAFE only for Postgres 9.6 or later.
Using a polymorphic input type this works for any array type, not just int[].
Make it IMMUTABLE to allow performance optimization and index expressions.
Does PostgreSQL support "accent insensitive" collations?
But don't make it STRICT, which would disable "function inlining" and impair performance because array_position() is not STRICT itself. See:
Function executes faster without STRICT modifier?
If you need to catch the case arr IS NULL:
CREATE OR REPLACE FUNCTION f_array_has_null (anyarray)
RETURNS bool
LANGUAGE sql IMMUTABLE PARALLEL SAFE AS
'SELECT CASE WHEN $1 IS NOT NULL
THEN array_position($1, NULL) IS NOT NULL END';
For Postgres 9.1 use the t_91 expression from above. The rest applies unchanged.
Closely related:
How to determine if NULL is contained in an array in Postgres?

Answer 2

PostgreSQL's UNNEST() function is a better choice.You can write a simple function like below to check for NULL values in an array.
create or replace function NULL_EXISTS(val anyelement) returns boolean as
$$
select exists (
select 1 from unnest(val) arr(el) where el is null
);
$$
language sql
For example,
SELECT NULL_EXISTS(array [1,2,NULL])
,NULL_EXISTS(array [1,2,3]);
Result:
null_exists null_exists
----------- --------------
t f
So, You can use NULL_EXISTS() function in your query like below.
SELECT num, ar, expected,NULL_EXISTS(ar)
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;

Answer 3

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)

Answer 4

I use this
select
array_position(array[1,null], null) is not null
array_position - returns the subscript of the first occurrence of the second argument in the array, starting at the element indicated by the third argument or at the first element (array must be one-dimensional)