On Fri, 25 Jun 2004 08:16:47 +0400, sad <[EMAIL PROTECTED]> wrote:
> > Very simply, a boolean may have to values: true or false. It's also
> > possible that it's not been set to anything (NULL).
> really ?
> what about (13 < NULL)::BOOL
Per the semantics of NULL, 13 is neither greater than nor less than
NULL. NULL is the *unknown* value; it's impossible to meaningfully
compare it to anything else. Try (NULL = NULL)::boolean. It's NULL,
also.
Since no value, including NULL, is in any way definitively comparable
to NULL -- the unknown value -- comparing to NULL results in ...
unknown.
Otherwise known as NULL.
/rls
--
:wq
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TIP 9: the planner will ignore your desire to choose an index scan if your
joining column's datatypes do not match
