On Mon, Jul 30, 2012 at 9:34 PM, Leon Smith
So can the types that can be array elements be extended in any way, or are these types set in stone? (without modifying the PostgreSQL source itself, of course...) And if the array elements are set, does 9.2 support arrays of range types?
(The following is tested with PostgreSQL 8.4.11) Take a look in the system catalog:
SELECT oid, typname, typcategory, typarray FROM pg_type; oid | typname | typcategory | typarray --------+-----------------------------------+-------------+---------- 16 | bool | B | 1000 17 | bytea | U | 1001 18 | char | S | 1002 19 | name | S | 1003 20 | int8 | N | 1016 21 | int2 | N | 1005 22 | int2vector | A | 1006 23 | int4 | N | 1007 --- snip --- 1000 | _bool | A | 0 1001 | _bytea | A | 0 1002 | _char | A | 0 1003 | _name | A | 0 1005 | _int2 | A | 0 1006 | _int2vector | A | 0 1007 | _int4 | A | 0 --- snip ---
Every type has a corresponding array type. When a new type is created, a corresponding array type is also created in pg_type. Tables are types, too, and have corresponding array types. It appears int2vector and oidvector are regular value types, but overload the ARRAY[] notation and try to act like arrays. Read on for more details. Apparently, int2vector, which is an array-like type, has a corresponding type _int2vector. This means you can have an array of int2vectors: > SELECT '{1 2,3 4 5,6 7 8 9}'::int2vector[]; int2vector --------------------------- {"1 2","3 4 5","6 7 8 9"} Notice that each int2vector is independent; no dimension constraining is happening. However, the ARRAY syntax appears to be overloaded for int2vector: > SELECT ARRAY[1,2,3] :: int2vector; array ------- 1 2 3 (1 row) But notice the following: > SELECT ARRAY['1 2', '3 4 5', '6 7 8']::int2vector[]; array ------------------------- {"1 2","3 4 5","6 7 8"} (1 row) > SELECT ARRAY['23 45' :: int2vector, '67 89' :: int2vector]; array ------- 1 0 (1 row) The first example works as expected (under our assumption that int2vector is a regular type and not an array type), but the last example yields the wrong type (int2vector instead of int2vector[]) and produces garbage. This appears to be the case even with recent Postgres. If you want to support an array of int2vectors, leave off the signatures to work around the bug described above. -Joey