John Siracusa <[EMAIL PROTECTED]> writes:
> So apparently all I can do is find out if it's a null test, but not if it is
> specifically "IS NOT NULL"

No, because once you have determined that the node really IsA NullTest,
you can cast the pointer to (NullTest *) and look at the
NullTest-specific fields.  Think of this as poor man's object-oriented
programming: Node is the supertype of Expr which is the supertype of
NullTest (and a lot of other kinds of nodes, too).

It'd look something like

        if (IsA(predicate, NullTest) &&
            ((NullTest *) predicate)->nulltesttype == IS_NOT_NULL)
          /* check to see if arg field matches either side of opclause,
           * and if so check whether operator is strict ...

You can find plenty of examples of this programming pattern throughout
the backend.  In fact pred_test_simple_clause is doing exactly this
to check that what it's given is an OpExpr and not some other node type.

                        regards, tom lane

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