auto merge

mysql-test/r/having.result

@@ -424,3 +424,10 @@ select f1 from t1 group by f1 having max(f1)=f1;
 f1
 set session sql_mode='';
 drop table t1;
+CREATE TABLE t1 ( a INT, b INT);
+INSERT INTO t1 VALUES (1, 1), (2,2), (3, NULL);
+SELECT b, COUNT(DISTINCT a) FROM t1 GROUP BY b HAVING b is NULL;
+b	COUNT(DISTINCT a)
+NULL	1
+DROP TABLE t1;
+End of 5.0 tests

mysql-test/t/having.test

@@ -432,3 +432,14 @@ select f1 from t1 having max(f1)=f1;
 select f1 from t1 group by f1 having max(f1)=f1;
 set session sql_mode='';
 drop table t1;
+
+
+#
+# Bug #38637: COUNT DISTINCT prevents NULL testing in HAVING clause
+#
+CREATE TABLE t1 ( a INT, b INT);
+INSERT INTO t1 VALUES (1, 1), (2,2), (3, NULL);
+SELECT b, COUNT(DISTINCT a) FROM t1 GROUP BY b HAVING b is NULL;
+DROP TABLE t1;
+
+--echo End of 5.0 tests

sql/item.cc

@@ -2041,6 +2041,12 @@ bool Item_field::val_bool_result()
 }
 
 
+bool Item_field::is_null_result()
+{
+  return (null_value=result_field->is_null());
+}
+
+
 bool Item_field::eq(const Item *item, bool binary_cmp) const
 {
   Item *real_item= ((Item *) item)->real_item();
@@ -5629,6 +5635,15 @@ double Item_ref::val_result()
 }
 
 
+bool Item_ref::is_null_result()
+{
+  if (result_field)
+    return (null_value=result_field->is_null());
+
+  return is_null();
+}
+
+
 longlong Item_ref::val_int_result()
 {
   if (result_field)
@@ -5734,7 +5749,9 @@ String *Item_ref::val_str(String* tmp)
 bool Item_ref::is_null()
 {
   DBUG_ASSERT(fixed);
-  return (*ref)->is_null();
+  bool tmp=(*ref)->is_null_result();
+  null_value=(*ref)->null_value;
+  return tmp;
 }
 
 

sql/item.h

@@ -652,6 +652,7 @@ public:
   virtual my_decimal *val_decimal_result(my_decimal *val)
   { return val_decimal(val); }
   virtual bool val_bool_result() { return val_bool(); }
+  virtual bool is_null_result() { return is_null(); }
 
   /* bit map of tables used by item */
   virtual table_map used_tables() const { return (table_map) 0L; }
@@ -1301,6 +1302,7 @@ public:
   String *str_result(String* tmp);
   my_decimal *val_decimal_result(my_decimal *);
   bool val_bool_result();
+  bool is_null_result();
   bool send(Protocol *protocol, String *str_arg);
   void reset_field(Field *f);
   bool fix_fields(THD *, Item **);
@@ -1942,6 +1944,7 @@ public:
   String *str_result(String* tmp);
   my_decimal *val_decimal_result(my_decimal *);
   bool val_bool_result();
+  bool is_null_result();
   bool send(Protocol *prot, String *tmp);
   void make_field(Send_field *field);
   bool fix_fields(THD *, Item **);

sql/item_func.cc

@@ -4285,6 +4285,15 @@ my_decimal *Item_func_set_user_var::val_decimal_result(my_decimal *val)
 }
 
 
+bool Item_func_set_user_var::is_null_result()
+{
+  DBUG_ASSERT(fixed == 1);
+  check(TRUE);
+  update();					// Store expression
+  return is_null();
+}
+
+
 void Item_func_set_user_var::print(String *str)
 {
   str->append(STRING_WITH_LEN("(@"));

sql/item_func.h

@@ -1302,6 +1302,7 @@ public:
   longlong val_int_result();
   String *str_result(String *str);
   my_decimal *val_decimal_result(my_decimal *);
+  bool is_null_result();
   bool update_hash(void *ptr, uint length, enum Item_result type,
   		   CHARSET_INFO *cs, Derivation dv, bool unsigned_arg);
   bool send(Protocol *protocol, String *str_arg);