Re: [PERFORM] Feature request: smarter use of conditional indexes

On 3/3/04 6:53 PM, Tom Lane wrote:
>  John Siracusa <siracusa@mindspring.com> writes:
>>  Given an index like this:
>>      CREATE UNIQUE INDEX i1 ON t1 (c1) WHERE c1 IS NOT NULL;
>>  and a query like this:
>>      SELECT * FROM t1 WHERE c1 = 123;
>>  I'd like the planner to be smart enough to use an index scan using
>> i1.
>
>  Send a patch ;-)

(Originally sent to the wrong list and in the wrong format...sorry :)

How does this look?  It seems to do what I want without horribly
breaking anything as far as I can tell.  I ran "make check" and got the
same result as I did before my changes (5 failures in OS X 10.3.2).
But then, I also got the same result when I wasn't even checking to
make sure that both clauses were looking at the same variable :)  I'm
not sure how to add a test for this particular change either.

Index: src/backend/optimizer/path/indxpath.c
===================================================================
RCS file:
/projects/cvsroot/pgsql-server/src/backend/optimizer/path/indxpath.c,v
retrieving revision 1.156
diff -c -r1.156 indxpath.c
*** src/backend/optimizer/path/indxpath.c    7 Jan 2004 22:02:48
-0000    1.156
--- src/backend/optimizer/path/indxpath.c    7 Mar 2004 03:49:17 -0000
***************
*** 1030,1036 ****
--- 1030,1060 ----
        * the test operator will always be strict.
        */
       if (!is_opclause(predicate))
+     {
+         /* One last chance: "var = const" or "const = var" implies "var is
not null" */
+         if (IsA(predicate, NullTest) &&
+             ((NullTest *) predicate)->nulltesttype == IS_NOT_NULL &&
+             is_opclause(clause) && op_strict(((OpExpr *) clause)->opno) &&
+             length(((OpExpr *) clause)->args) == 2)
+         {
+             leftop = get_leftop((Expr *) clause);
+             rightop = get_rightop((Expr *) clause);
+
+             /* One of the two arguments must be a constant */
+             if (IsA(rightop, Const))
+                 clause_var = leftop;
+             else if (IsA(leftop, Const))
+                 clause_var = rightop;
+             else
+                 return false;
+
+             /* Finally, make sure "var" is the same var in both clauses */
+             if (equal(((NullTest *) predicate)->arg, clause_var))
+                 return true;
+         }
+
           return false;
+     }
       leftop = get_leftop(predicate);
       rightop = get_rightop(predicate);
       if (rightop == NULL)