bk commit into 5.0 tree (sergefp:1.2120) BUG#16798

[Sergey Petrunia]

Below is the list of changes that have just been committed into a local
5.0 repository of psergey. When psergey does a push these changes will
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ChangeSet
  1.2120 06/05/07 19:01:49 sergefp@stripped +1 -0
  BUG#16798: Merge into 5.0: s/used_tables()/!const_item()/, added comment about its
effects.

  sql/sql_select.cc
    1.411 06/05/07 19:01:43 sergefp@stripped +14 -2
    BUG#16798: Merge into 5.0: s/used_tables()/!const_item()/, added comment about its
effects.

# This is a BitKeeper patch.  What follows are the unified diffs for the
# set of deltas contained in the patch.  The rest of the patch, the part
# that BitKeeper cares about, is below these diffs.
# User:	sergefp
# Host:	newbox.mylan
# Root:	/home/psergey/mysql-5.0-bug16798-merge

--- 1.410/sql/sql_select.cc	2006-05-06 13:19:05 +04:00
+++ 1.411/sql/sql_select.cc	2006-05-07 19:01:43 +04:00
@@ -2377,7 +2377,19 @@
     {
       if (old->field == new_fields->field)
       {
-	if (new_fields->val->used_tables())
+        /*
+          NOTE: below const_item() call really works as "!used_tables()", i.e.
+          it can return FALSE where it is feasible to make it return TRUE.
+          
+          The cause is as follows: Some of the tables are already known to be
+          const tables (the detection code is in make_join_statistics(),
+          above the update_ref_and_keys() call), but we didn't propagate 
+          information about this: TABLE::const_table is not set to TRUE, and
+          Item::update_used_tables() hasn't been called for each item.
+          The result of this is that we're missing some 'ref' accesses.
+          TODO: OptimizerTeam: Fix this
+        */
+	if (!new_fields->val->const_item())
 	{
 	  /*
 	    If the value matches, we can use the key reference.
@@ -2407,7 +2419,7 @@
                                 new_fields->null_rejecting);
 	}
 	else if (old->eq_func && new_fields->eq_func &&
-		 ((!old->val->used_tables() && old->val->is_null()) || 
+		 ((old->val->const_item() && old->val->is_null()) || 
                   new_fields->val->is_null()))
 	{
 	  /* field = expression OR field IS NULL */