Re: [HACKERS] IS OF

Bruce Momjian wrote:
> Can someone suggest where to document IS OF, and either document it's
> non-standard behavior or supply patch?
>

Doc patch attached for IS OF. Please apply.

Thanks,

Joe

> ---------------------------------------------------------------------------
>
> Joe Conway wrote:
>
>>Gavin Sherry wrote:
>>
>>>8.14 <type predicate> to be exact.
>>>
>>
>>8.18 in SQL200x. I don't think the current implementation quite meets
>>the spec however:
>>
>>regression=# select f2 is null, f2 is of(int) from bar;
>> ?column? | ?column?
>>----------+----------
>> f | t
>> t | t
>>(2 rows)
>>
>>If I read the spec correctly, the null value should return null, not 't'
>>in the above.
>>
>>General Rules
>>1) Let V be the result of evaluating the <row value predicand>.
>>2) Let ST be the set consisting of every type that is either some
>> exclusively specified type, or a subtype of some inclusively
>> specified type.
>>3) Let TPR be the result of evaluating the <type predicate>.
>>
>>Case:
>>a) If V is the null value, then TPR is Unknown.
>>b) If the most specific type of V is a member of ST, then TPR is True .
>>c) Otherwise, TPR is False
>>