Павел Воронцов,
ну вы и загнули, ведь pg_group - системная таблица постгреса, не желаете исправить???

Но в общем надо читать доки, вот что там:

To search for a value in an array, you must check each value of the array. This can be done by hand (if you know the size of the array):

SELECT * FROM sal_emp WHERE pay_by_quarter[1] = 10000 OR
pay_by_quarter[2] = 10000 OR
pay_by_quarter[3] = 10000 OR
pay_by_quarter[4] = 10000;

However, this quickly becomes tedious for large arrays, and is not helpful if the size of the array is unknown. Although it is not part of the primary PostgreSQL distribution, there is an extension available that defines new functions and operators for iterating over array values. Using this, the above query could be:

SELECT * FROM sal_emp WHERE pay_by_quarter[1:4] *= 10000;

To search the entire array (not just specified columns), you could use:

SELECT * FROM sal_emp WHERE pay_by_quarter *= 10000;

In addition, you could find rows where the array had all values equal to 10 000 with:

SELECT * FROM sal_emp WHERE pay_by_quarter **= 10000;

To install this optional module, look in the contrib/array directory of the PostgreSQL source distribution.
Так что ставь модуль и живи спокойно :)