Check if value exists in Postgres array

Question

I need a way to test if a value exists in a given array. So far I came up with something like this

select '{1,2,3}'::int[] @> (ARRAY[]::int[] || value_variable::int)

but I keep thinking there should be a simpler way to this, I just cant see it.

Edit: Just realized I could do this

select '{1,2,3}'::int[] @> ARRAY[value_variable::int]

This is much better and I believe will suffice, but if you have other ways to do it please share.

Answer 1

When looking for the existence of a element in an array, proper casting is required to pass the SQL parser of postgres. Here is one example query using array contains operator in the join clause:

For simplicity I only list the relevant part:

table1 other_name text[]; -- is an array of text

The join part of SQL shown

from table1 t1 join table2 t2 on t1.other_name::text[] @> ARRAY[t2.panel::text]

The following also works

on t2.panel = ANY(t1.other_name)

I am just guessing that the extra casting is required because the parse does not have to fetch the table definition to figure the exact type of the column. Others please comment on this.

Answer 2

but if you have other ways to do it please share.

You can compare two arrays. If any of the values in the left array overlap the values in the right array, then it returns true. It's kind of hackish, but it works.

SELECT '{1}'   && '{1,2,3}'::int[];  -- true
SELECT '{1,4}' && '{1,2,3}'::int[];  -- true
SELECT '{4}'   && '{1,2,3}'::int[];  -- false

• In the first and second query, value 1 is in the right array
• Notice that the second query is true, even though the value 4 is not contained in the right array
• For the third query, no values in the left array (i.e., 4) are in the right array, so it returns false

Answer 3

Simpler with the ANY construct:

SELECT value_variable = ANY ('{1,2,3}'::int[])

The right operand of ANY (between parentheses) can either be a set (result of a subquery, for instance) or an array. There are several ways to use it:

• SQLAlchemy: how to filter on PgArray column types?

Important difference: Array operators (<@, @> et al.) expect array types as operands and support GIN or GiST indices in the standard distribution of PostgreSQL, while the ANY construct expects an element type as left operand and does not support these indices. Example:

• Index for finding an element in a JSON array

None of this works for NULL elements. To test for NULL:

• Check if NULL exists in Postgres array

Answer 4

Watch out for the trap I got into: When checking if certain value is not present in an array, you shouldn't do:

SELECT value_variable != ANY('{1,2,3}'::int[])

but use

SELECT value_variable != ALL('{1,2,3}'::int[])

instead.

Answer 5

unnest can be used as well. It expands array to a set of rows and then simply checking a value exists or not is as simple as using IN or NOT IN.

e.g.

1. id => uuid

2. exception_list_ids => uuid[]

select * from table where id NOT IN (select unnest(exception_list_ids) from table2)