textの場合　

postgres=# CREATE TABLE test (
    sample text CONSTRAINT check_invalid_char CHECK (sample !~ 'a')
);
postgres=# INSERT INTO test VALUES ('hoge');
postgres=# INSERT INTO test VALUES ('hage');
ERROR:  new row for relation "test" violates check constraint "check_invalid_char"
DETAIL:  Failing row contains (hage).

text配列の場合

postgres=# CREATE FUNCTION check_text_value (
     vals text[]
) RETURNS boolean AS $$
     SELECT bool_and (t !~ 'a') FROM unnest(vals) AS t
$$ LANGUAGE sql IMMUTABLE
postgresql=# CREATE TABLE test (
    text[] vals CHECK (check_text_value (vals))
);

参考