MDEV-4284 Assertion `cmp_items[(uint)cmp_type]' fails in sql/item_cmpfunc.cc

Flip the switch and create Item_cache based on the argument's cmp_type, not argument's result_type().
Fix subselect_engine to calculate cmp_type correctly

sql/item_subselect.h:
  mdev:4284

mysql-test/r/cache_temporal_4265.result

@@ -7,5 +7,4 @@ a
 2002-03-04
 Warnings:
 Note	1003	2000-01-01
-Note	1003	2000-01-06
 drop table t1;

mysql-test/r/func_date_add.result

@@ -96,3 +96,9 @@ b + interval a day
 2002-02-04
 drop table t1;
 End of 5.0 tests
+create table t1 (a varchar(10));
+insert t1 values ('2000-12-03'),('2008-05-03');
+select * from t1 where case a when adddate( '2012-12-12', 7 ) then true end;
+a
+drop table t1;
+End of 5.5 tests

mysql-test/t/func_date_add.test

@@ -88,3 +88,15 @@ select b + interval a day from t1;
 drop table t1;
 
 --echo End of 5.0 tests
+
+#
+# MDEV-4284 Assertion `cmp_items[(uint)cmp_type]' fails in sql/item_cmpfunc.cc
+#
+
+create table t1 (a varchar(10));
+insert t1 values ('2000-12-03'),('2008-05-03');
+select * from t1 where case a when adddate( '2012-12-12', 7 ) then true end;
+drop table t1;
+
+--echo End of 5.5 tests
+

sql/item.cc

@@ -8643,7 +8643,7 @@ int stored_field_cmp_to_item(THD *thd, Field *field, Item *item)
 
 Item_cache* Item_cache::get_cache(const Item *item)
 {
-  return get_cache(item, item->result_type());
+  return get_cache(item, item->cmp_type());
 }
 
 

sql/item_subselect.cc

@@ -1087,6 +1087,11 @@ enum Item_result Item_singlerow_subselect::result_type() const
   return engine->type();
 }
 
+enum Item_result Item_singlerow_subselect::cmp_type() const
+{
+  return engine->cmptype();
+}
+
 /* 
  Don't rely on the result type to calculate field type. 
  Ask the engine instead.
@@ -3044,12 +3049,13 @@ void subselect_engine::set_row(List<Item> &item_list, Item_cache **row)
 {
   Item *sel_item;
   List_iterator_fast<Item> li(item_list);
-  res_type= STRING_RESULT;
+  cmp_type= res_type= STRING_RESULT;
   res_field_type= MYSQL_TYPE_VAR_STRING;
   for (uint i= 0; (sel_item= li++); i++)
   {
     item->max_length= sel_item->max_length;
     res_type= sel_item->result_type();
+    cmp_type= sel_item->cmp_type();
     res_field_type= sel_item->field_type();
     item->decimals= sel_item->decimals;
     item->unsigned_flag= sel_item->unsigned_flag;
@@ -3060,7 +3066,7 @@ void subselect_engine::set_row(List<Item> &item_list, Item_cache **row)
  //psergey-backport-timours:   row[i]->store(sel_item);
   }
   if (item_list.elements > 1)
-    res_type= ROW_RESULT;
+    cmp_type= res_type= ROW_RESULT;
 }
 
 void subselect_single_select_engine::fix_length_and_dec(Item_cache **row)

sql/item_subselect.h

@@ -286,6 +286,7 @@ public:
   bool val_bool();
   bool get_date(MYSQL_TIME *ltime, ulonglong fuzzydate);
   enum Item_result result_type() const;
+  enum Item_result cmp_type() const;
   enum_field_types field_type() const;
   void fix_length_and_dec();
 
@@ -698,6 +699,7 @@ protected:
   THD *thd; /* pointer to current THD */
   Item_subselect *item; /* item, that use this engine */
   enum Item_result res_type; /* type of results */
+  enum Item_result cmp_type; /* how to compare the results */
   enum_field_types res_field_type; /* column type of the results */
   bool maybe_null; /* may be null (first item in select) */
 public:
@@ -712,7 +714,7 @@ public:
   {
     result= res;
     item= si;
-    res_type= STRING_RESULT;
+    cmp_type= res_type= STRING_RESULT;
     res_field_type= MYSQL_TYPE_VAR_STRING;
     maybe_null= 0;
     set_thd(thd_arg);
@@ -752,6 +754,7 @@ public:
   virtual uint cols()= 0; /* return number of columns in select */
   virtual uint8 uncacheable()= 0; /* query is uncacheable */
   enum Item_result type() { return res_type; }
+  enum Item_result cmptype() { return cmp_type; }
   enum_field_types field_type() { return res_field_type; }
   virtual void exclude()= 0;
   virtual bool may_be_null() { return maybe_null; };