Bug #11032: getObject() returns a String for a sub-query of type datetime

 - When returning metadata for scalar subqueries the actual type of the
   column was calculated based on the value type, which limits the actual
   type of a scalar subselect to the set of (currently) 3 basic types : 
   integer, double precision or string. This is the reason that columns
   of types other then the basic ones (e.g. date/time) are reported as
   being of the corresponding basic type.
   Fixed by storing/returning information for the column type in addition
   to the result type.

mysql-test/r/subselect.result

@@ -2997,3 +2997,20 @@ a	a IN (SELECT a FROM t1)
 2	NULL
 3	1
 DROP TABLE t1,t2;
+CREATE TABLE t1 (a DATETIME);
+INSERT INTO t1 VALUES ('1998-09-23'), ('2003-03-25');
+CREATE TABLE t2 AS SELECT 
+(SELECT a FROM t1 WHERE a < '2000-01-01') AS sub_a 
+FROM t1 WHERE a > '2000-01-01';
+SHOW CREATE TABLE t2;
+Table	Create Table
+t2	CREATE TABLE `t2` (
+  `sub_a` datetime default NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+CREATE TABLE t3 AS (SELECT a FROM t1 WHERE a < '2000-01-01') UNION (SELECT a FROM t1 WHERE a > '2000-01-01');
+SHOW CREATE TABLE t3;
+Table	Create Table
+t3	CREATE TABLE `t3` (
+  `a` datetime default NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+DROP TABLE t1,t2,t3;

mysql-test/t/subselect.test

@@ -1965,4 +1965,20 @@ SELECT a, a IN (SELECT a FROM t1) FROM t2;
 
 DROP TABLE t1,t2;
 
+#
+# Bug #11302: getObject() returns a String for a sub-query of type datetime
+#
+CREATE TABLE t1 (a DATETIME);
+INSERT INTO t1 VALUES ('1998-09-23'), ('2003-03-25');
+
+CREATE TABLE t2 AS SELECT 
+  (SELECT a FROM t1 WHERE a < '2000-01-01') AS sub_a 
+   FROM t1 WHERE a > '2000-01-01';
+SHOW CREATE TABLE t2;
+
+CREATE TABLE t3 AS (SELECT a FROM t1 WHERE a < '2000-01-01') UNION (SELECT a FROM t1 WHERE a > '2000-01-01'); 
+SHOW CREATE TABLE t3;
+
+DROP TABLE t1,t2,t3;
+
 # End of 4.1 tests

sql/item_subselect.cc

@@ -391,6 +391,15 @@ enum Item_result Item_singlerow_subselect::result_type() const
   return engine->type();
 }
 
+/* 
+ Don't rely on the result type to calculate field type. 
+ Ask the engine instead.
+*/
+enum_field_types Item_singlerow_subselect::field_type() const
+{
+  return engine->field_type();
+}
+
 void Item_singlerow_subselect::fix_length_and_dec()
 {
   if ((max_columns= engine->cols()) == 1)
@@ -1357,31 +1366,35 @@ int subselect_uniquesubquery_engine::prepare()
   return 1;
 }
 
-static Item_result set_row(List<Item> &item_list, Item *item,
-			   Item_cache **row, bool *maybe_null)
+/* 
+ makes storage for the output values for the subquery and calcuates 
+ their data and column types and their nullability.
+*/ 
+void subselect_engine::set_row(List<Item> &item_list, Item_cache **row)
 {
-  Item_result res_type= STRING_RESULT;
   Item *sel_item;
   List_iterator_fast<Item> li(item_list);
+  res_type= STRING_RESULT;
+  res_field_type= FIELD_TYPE_VAR_STRING;
   for (uint i= 0; (sel_item= li++); i++)
   {
     item->max_length= sel_item->max_length;
     res_type= sel_item->result_type();
+    res_field_type= sel_item->field_type();
     item->decimals= sel_item->decimals;
-    *maybe_null= sel_item->maybe_null;
+    maybe_null= sel_item->maybe_null;
     if (!(row[i]= Item_cache::get_cache(res_type)))
-      return STRING_RESULT; // we should return something
+      return;
     row[i]->setup(sel_item);
   }
   if (item_list.elements > 1)
     res_type= ROW_RESULT;
-  return res_type;
 }
 
 void subselect_single_select_engine::fix_length_and_dec(Item_cache **row)
 {
   DBUG_ASSERT(row || select_lex->item_list.elements==1);
-  res_type= set_row(select_lex->item_list, item, row, &maybe_null);
+  set_row(select_lex->item_list, row);
   item->collation.set(row[0]->collation);
   if (cols() != 1)
     maybe_null= 0;
@@ -1393,13 +1406,14 @@ void subselect_union_engine::fix_length_and_dec(Item_cache **row)
 
   if (unit->first_select()->item_list.elements == 1)
   {
-    res_type= set_row(unit->types, item, row, &maybe_null);
+    set_row(unit->types, row);
     item->collation.set(row[0]->collation);
   }
   else
   {
-    bool fake= 0;
-    res_type= set_row(unit->types, item, row, &fake);
+    bool maybe_null_saved= maybe_null;
+    set_row(unit->types, row);
+    maybe_null= maybe_null_saved;
   }
 }
 

sql/item_subselect.h

@@ -142,6 +142,7 @@ public:
   longlong val_int ();
   String *val_str (String *);
   enum Item_result result_type() const;
+  enum_field_types field_type() const;
   void fix_length_and_dec();
 
   uint cols();
@@ -273,6 +274,7 @@ protected:
   THD *thd; /* pointer to current THD */
   Item_subselect *item; /* item, that use this engine */
   enum Item_result res_type; /* type of results */
+  enum_field_types res_field_type; /* column type of the results */
   bool maybe_null; /* may be null (first item in select) */
 public:
 
@@ -282,6 +284,7 @@ public:
     result= res;
     item= si;
     res_type= STRING_RESULT;
+    res_field_type= FIELD_TYPE_VAR_STRING;
     maybe_null= 0;
   }
   virtual ~subselect_engine() {}; // to satisfy compiler
@@ -296,6 +299,7 @@ public:
   virtual uint cols()= 0; /* return number of columnss in select */
   virtual uint8 uncacheable()= 0; /* query is uncacheable */
   enum Item_result type() { return res_type; }
+  enum_field_types field_type() { return res_field_type; }
   virtual void exclude()= 0;
   bool may_be_null() { return maybe_null; };
   virtual table_map upper_select_const_tables()= 0;
@@ -303,6 +307,9 @@ public:
   virtual void print(String *str)= 0;
   virtual int change_item(Item_subselect *si, select_subselect *result)= 0;
   virtual bool no_tables()= 0;
+
+protected:
+  void set_row(List<Item> &item_list, Item_cache **row);
 };