fixed an obscure bug in group by + having + Item_ref::get_date

mysql-test/r/group_by.result

@@ -128,3 +128,4 @@ a	MAX(b)	ELT(MAX(b), 'a', 'b', 'c', 'd', 'e', 'f')
 a	MAX(b)	MAKE_SET(MAX(b), 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h')
 1	4	c
 10	43	a,b,d,f
+a	c	count(distinct rand())

mysql-test/t/group_by.test

@@ -346,3 +346,11 @@ select a, MAX(b), CONCAT_WS(MAX(b), '43', '4', '5') from t1 group by a;
 select a, MAX(b), ELT(MAX(b), 'a', 'b', 'c', 'd', 'e', 'f') from t1 group by a;
 select a, MAX(b), MAKE_SET(MAX(b), 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h') from t1 group by a;
 drop table t1;
+
+# not purely group_by bug, but group_by is involved...
+
+create table t1 (a date default null, b date default null);
+insert t1 values ('1999-10-01','2000-01-10'), ('1997-01-01','1998-10-01');
+select a,min(b) c,count(distinct rand()) from t1 group by a having c<a + interval 1 day;
+drop table t1;
+

sql/item.cc

@@ -194,6 +194,17 @@ bool Item_field::get_date(TIME *ltime,bool fuzzydate)
   return 0;
 }
 
+bool Item_field::get_date_result(TIME *ltime,bool fuzzydate)
+{
+  if ((null_value=result_field->is_null()) ||
+      result_field->get_date(ltime,fuzzydate))
+  {
+    bzero((char*) ltime,sizeof(*ltime));
+    return 1;
+  }
+  return 0;
+}
+
 bool Item_field::get_time(TIME *ltime)
 {
   if ((null_value=field->is_null()) || field->get_time(ltime))

sql/item.h

@@ -82,6 +82,8 @@ class Item {
   virtual void split_sum_func(List<Item> &fields) {}
   virtual bool get_date(TIME *ltime,bool fuzzydate);
   virtual bool get_time(TIME *ltime);
+  virtual bool get_date_result(TIME *ltime,bool fuzzydate)
+  { return get_date(ltime,fuzzydate); }
 };
 
 
@@ -130,6 +132,7 @@ class Item_field :public Item_ident
   }
   Field *tmp_table_field() { return result_field; }
   bool get_date(TIME *ltime,bool fuzzydate);
+  bool get_date_result(TIME *ltime,bool fuzzydate);
   bool get_time(TIME *ltime);
 };
 
@@ -333,7 +336,7 @@ class Item_ref :public Item_ident
   }
   bool get_date(TIME *ltime,bool fuzzydate)
   {
-    return (null_value=(*ref)->get_date(ltime,fuzzydate));
+    return (null_value=(*ref)->get_date_result(ltime,fuzzydate));
   }
   bool send(String *tmp)		{ return (*ref)->send(tmp); }
   void make_field(Send_field *field)	{ (*ref)->make_field(field); }