Re: AW: Re: [SQL] behavior of ' = NULL' vs. MySQL vs. Stand ards - Mailing list pgsql-hackers

"Joe Conway" <joseph.conway@home.com> writes:
> I also noticed that in PostgreSQL I can do the following (both before and
> after this patch):
>     select f2 is null from foo;
> whereas in both Oracle and MSSQL it causes a syntax error. Any thoughts on
> this?

I dug into this further and discovered that indeed it is not SQL92
... but it is SQL99.  Amazingly enough, SQL92 doesn't allow boolean
expressions as a possible type of general expression:
        <value expression> ::=               <numeric value expression>             | <string value expression>
   | <datetime value expression>             | <interval value expression>
 

It only allows them as <search condition>s, which is to say WHERE,
HAVING, CASE WHEN, CHECK, and one or two other places.

But SQL99 gets it right:
        <value expression> ::=               <numeric value expression>             | <string value expression>
   | <datetime value expression>             | <interval value expression>             | <boolean value expression>
       | <user-defined type value expression>             | <row value expression>             | <reference value
expression>            | <collection value expression>
 

Looks like we're ahead of the curve here...
        regards, tom lane