Hi, I have a question.
As I noted that (null,null) is null, I thought why put (null,null) in an array when that is the same as putting null in there. However, when trying to unnest that array I got an error when using null instead of the tuple. I experimented a bit, and read the documentation on row and array comparison, but I could not find documentation explaining the results below. create type int_tuple as (a int, b int); CREATE TYPE =# select (null,null)::int_tuple is null; ?column? ---------- t (1 row) =# select array[null::int_tuple] = array[null::int_tuple]; ?column? ---------- t (1 row) as the documentation states: 'Array comparisons compare the array contents element-by-element' Taking into account the results above I would expect the following to be true =# select array[(null,null)::int_tuple] = array[null::int_tuple]; ?column? ---------- f (1 row) apparently (null,null) is has more information then just null: =# select null::int_tuple; int_tuple ----------- (1 row) =# select (null,null)::int_tuple; row ----- (,) (1 row) =# select * from unnest(array[null::int_tuple]); ERROR: function returning set of rows cannot return null value =# select * from unnest(array[(null,null)::int_tuple]); a | b ---+--- | (1 row) Can anyone explain why: create type int_tuple as (a int, b int); CREATE TYPE =# select (null,null)::int_tuple is null; ?column? ---------- t (1 row) and not =# select array[(null,null)::int_tuple] = array[null::int_tuple]; ?column? ---------- f (1 row) Thanks in advance, Ingmar version -------------------------------------------------------------------------------------------------------------- PostgreSQL 9.1.1 on x86_64-unknown-linux-gnu, compiled by gcc (GCC) 4.6.1 20110908 (Red Hat 4.6.1-9), 64-bit (1 row)
