two tables:

t1: id, x1 (integer)
t2: id, a2 (integer[])

The command:

SELECT id FROM t1s WHERE x1 IN (SELECT a2 FROM t2s WHERE id = #{id});

causes the ERROR:

operator does not exist: bigint = integer[]

The problem is caused by "SELECT a2 FROM t2s WHERE id = #{id}" returning an array of arrays (or maybe a list of arrays), but the "IN" command in the outer command is looking for an array of integers.

[a2] = SELECT a2 FROM t2s WHERE id = #{id}

would work if it's:

a2 = SELECT a2 FROM t2s WHERE id = #{id}

The problem remains the same if I tell psql that "(SELECT a2 FROM t2s WHERE id = #{id})" is only one row by "(SELECT a2 FROM t2s WHERE id = #{id} FETCH FIRST 1 ROW ONLY)"

So how to convert the list of arrays with one element "[a2]" to its single array element "a2"?