Bug #48458: simple query tries to allocate enormous amount of

  memory

The server was doing a bad class typecast causing setting of 
wrong value for the maximum number of items in an internal
structure used in equality propagation.
Fixed by not doing the wrong typecast and asserting the type
of the Item where it should be done.

mysql-test/r/select.result

@@ -4442,4 +4442,18 @@ ROW(a,a) <=> ROW((SELECT 1 FROM t1 WHERE 1=2),(SELECT 1 FROM t1))
 INTO @var0;
 ERROR 21000: Subquery returns more than 1 row
 DROP TABLE t1;
+#
+# Bug #48458: simple query tries to allocate enormous amount of
+#   memory
+#
+CREATE TABLE t1(a INT NOT NULL, b YEAR);
+INSERT INTO t1 VALUES ();
+Warnings:
+Warning	1364	Field 'a' doesn't have a default value
+CREATE TABLE t2(c INT);
+# Should not err out because of out-of-memory
+SELECT 1 FROM t2 JOIN t1 ON 1=1
+WHERE a != '1' AND NOT a >= b OR NOT ROW(b,a )<> ROW(a,a);
+1
+DROP TABLE t1,t2;
 End of 5.0 tests

mysql-test/t/select.test

@@ -3783,5 +3783,18 @@ INTO @var0;
 
 DROP TABLE t1;
  
+--echo #
+--echo # Bug #48458: simple query tries to allocate enormous amount of
+--echo #   memory
+--echo #
+
+CREATE TABLE t1(a INT NOT NULL, b YEAR);
+INSERT INTO t1 VALUES ();
+CREATE TABLE t2(c INT);
+--echo # Should not err out because of out-of-memory
+SELECT 1 FROM t2 JOIN t1 ON 1=1
+  WHERE a != '1' AND NOT a >= b OR NOT ROW(b,a )<> ROW(a,a);
+DROP TABLE t1,t2;
+
 
 --echo End of 5.0 tests

sql/sql_select.cc

@@ -7535,13 +7535,13 @@ static COND *build_equal_items_for_cond(THD *thd, COND *cond,
         {
           item_equal->fix_length_and_dec();
           item_equal->update_used_tables();
-	}
-        else
-          item_equal= (Item_equal *) eq_list.pop();
           set_if_bigger(thd->lex->current_select->max_equal_elems,
                         item_equal->members());  
           return item_equal;
 	}
+
+        return eq_list.pop();
+      }
       else
       {
         /*