MWL#90: Address review feedback part #18

sql/item_subselect.h

@@ -371,12 +371,6 @@ public:
     See also THD::emb_on_expr_nest.
   */
   TABLE_LIST *emb_on_expr_nest;
-  /* 
-    Location of the subquery predicate. It is either
-     - pointer to join nest if the subquery predicate is in the ON expression
-     - (TABLE_LIST*)1 if the predicate is in the WHERE.
-  */
-  //TABLE_LIST *expr_join_nest;
   /*
     Types of left_expr and subquery's select list allow to perform subquery
     materialization. Currently, we set this to FALSE when it as well could
@@ -403,6 +397,18 @@ public:
   */
   bool is_flattenable_semijoin;
 
+  /*
+    Used to determine how this subselect item is represented in the item tree,
+    in case there is a need to locate it there and replace with something else.
+    Two options are possible:
+      1. This item is there 'as-is'.
+      1. This item is wrapped within Item_in_optimizer.
+  */
+  Item *original_item()
+  {
+    return is_flattenable_semijoin ? (Item*)this : (Item*)optimizer;
+  }
+  
   bool *get_cond_guard(int i)
   {
     return pushed_cond_guards ? pushed_cond_guards + i : NULL;

sql/opt_subselect.cc

@@ -712,16 +712,7 @@ bool convert_join_subqueries_to_semijoins(JOIN *join)
     {
       Item **tree= ((*in_subq)->emb_on_expr_nest == NO_JOIN_NEST)?
                      &join->conds : &((*in_subq)->emb_on_expr_nest->on_expr);
-      Item *replace_me= *in_subq;
-      /*
-        JTBM: the subquery was already mapped with Item_in_optimizer, so we
-        should search for that, not for original Item_in_subselect.
-        TODO: what about delaying that rewrite until here?
-      */
-      if (!(*in_subq)->is_flattenable_semijoin)
-      {
-        replace_me= (*in_subq)->optimizer;
-      }
+      Item *replace_me= (*in_subq)->original_item();
       if (replace_where_subcondition(join, tree, replace_me, new Item_int(1),
                                      FALSE))
         DBUG_RETURN(TRUE); /* purecov: inspected */
@@ -756,18 +747,7 @@ skip_conversion:
     bool do_fix_fields= !(*in_subq)->substitution->fixed;
     Item **tree= ((*in_subq)->emb_on_expr_nest == NO_JOIN_NEST)?
                    &join->conds : &((*in_subq)->emb_on_expr_nest->on_expr);
-
-    Item *replace_me= *in_subq;
-    /*
-      JTBM: the subquery was already mapped with Item_in_optimizer, so we
-      should search for that, not for original Item_in_subselect.
-      TODO: what about delaying that rewrite until here?
-    */
-    if (!(*in_subq)->is_flattenable_semijoin)
-    {
-      replace_me= (*in_subq)->optimizer;
-    }
-
+    Item *replace_me= (*in_subq)->original_item();
     if (replace_where_subcondition(join, tree, replace_me, substitute, 
                                    do_fix_fields))
       DBUG_RETURN(TRUE);