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?
Postgres 9.1
If you know a single element that can never exist in your arrays, you can use this fast expression in Postgres 9.1 (or any version of Postgres). Say you have an array of positive numbers, so -1 can't be in it:
-1 = ANY(ar) IS NULL
Related answer with detailed explanation:
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(ar) x)
or:
EXISTS (SELECT 1 FROM unnest(ar) 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 ar IS NULL separately. See demo below.
Postgres 9.3
In Postgres 9.3 or later you can test with the built-in function array_remove() or array_replace() .
Postgres 9.5+
Or use array_position() in Postgres 9.5 or later like @Patrick added. I included improved variants.
Demo
SELECT num, ar, expect
, -1 = ANY(ar) IS NULL AS t_1 -- 50 ms
, (SELECT bool_or(x IS NULL) FROM unnest(ar) x) AS t_2 -- 754 ms
, EXISTS (SELECT 1 FROM unnest(ar) x WHERE x IS NULL) AS t_3 -- 521 ms
, CASE -1 = ANY(ar)
WHEN FALSE THEN FALSE
WHEN TRUE THEN EXISTS (SELECT 1 FROM unnest(ar) x WHERE x IS NULL)
ELSE NULLIF(ar IS NOT NULL, FALSE) -- catch ar IS NULL -- 55 ms
-- ELSE TRUE -- simpler for columns defined NOT NULL -- 51 ms
END AS t_91
, array_replace(ar, NULL, 0) <> ar AS t_93a -- 99 ms
, array_remove(ar, NULL) <> ar AS t_93b -- 96 ms
, cardinality(array_remove(ar, NULL)) <> cardinality(ar) AS t_94 -- 81 ms
, COALESCE(array_position(ar, NULL::int), 0) > 0 AS t_95a -- 49 ms
, array_position(ar, NULL) IS NOT NULL AS t_95b -- 45 ms
, CASE WHEN ar IS NOT NULL
THEN array_position(ar, 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, ar, expect);
Result:
num | ar | 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 11, with more tests).
Old sqlfiddle for Postgres 9.6.
Benchmark setup
The added times are from a benchmark test with 200k rows in Postgres 9.5. This is my setup:
CREATE TEMP TABLE t AS
SELECT row_number() OVER() AS num
, array_agg(elem) AS ar
, 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 AS
'SELECT array_position($1, NULL) IS NOT NULL';
Using a polymorphic input type this works for any array type, not just int[].
Make it IMMUTABLE to allow performance optimization and index expressions.
But don't make it STRICT, which would disable "function inlining" and impair performance.
If you need to catch the case ar IS NULL, instead of making the function STRICT, use:
CREATE OR REPLACE FUNCTION f_array_has_null (anyarray)
RETURNS bool LANGUAGE sql IMMUTABLE AS
'SELECT CASE WHEN $1 IS NOT NULL
THEN array_position($1, NULL) IS NOT NULL END';
For Postgres 9.1 use the t_91 expression from above. The rest applies unchanged.
Closely related:
PostgreSQL 9.5 (I know you spcified 9.1, but anyway) has the array_position() function to do just what you want without having to use the horribly inefficient unnest() for something as trivial as this (see test4):
patrick@puny:~$ 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)
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;
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)
来源：https://stackoverflow.com/questions/34848009/check-if-null-exists-in-postgres-array