Fix for bug #21976: Unnecessary warning with count(decimal)

We use val_int() calls (followed by null_value check) to determine 
nullness in some Item_sum_count' and Item_sum_count_distinct' methods, 
as a side effect we get extra warnings raised in the val_int().
Fix: use is_null() instead.

mysql-test/r/func_group.result

@@ -1029,3 +1029,13 @@ t1	CREATE TABLE `t1` (
   `stddev(0)` double(8,4) default NULL
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 drop table t1;
+create table t1 (a decimal(20));
+insert into t1 values (12345678901234567890);
+select count(a) from t1;
+count(a)
+1
+select count(distinct a) from t1;
+count(distinct a)
+1
+drop table t1;
+End of 5.0 tests

mysql-test/t/func_group.test

@@ -700,3 +700,14 @@ create table t1 select stddev(0);
 show create table t1;
 drop table t1;
  
+#
+# Bug #21976: Unnecessary warning with count(decimal)
+#
+
+create table t1 (a decimal(20));
+insert into t1 values (12345678901234567890);
+select count(a) from t1;
+select count(distinct a) from t1;
+drop table t1;
+
+--echo End of 5.0 tests

sql/item.h

@@ -701,12 +701,11 @@ public:
   virtual bool get_date_result(TIME *ltime,uint fuzzydate)
   { return get_date(ltime,fuzzydate); }
   /*
-    This function is used only in Item_func_isnull/Item_func_isnotnull
-    (implementations of IS NULL/IS NOT NULL clauses). Item_func_is{not}null
-    calls this method instead of one of val/result*() methods, which
-    normally will set null_value. This allows to determine nullness of
-    a complex expression without fully evaluating it.
-    Any new item which can be NULL must implement this call.
+    The method allows to determine nullness of a complex expression 
+    without fully evaluating it, instead of calling val/result*() then 
+    checking null_value. Used in Item_func_isnull/Item_func_isnotnull
+    and Item_sum_count/Item_sum_count_distinct.
+    Any new item which can be NULL must implement this method.
   */
   virtual bool is_null() { return 0; }
 

sql/item_sum.cc

@@ -1034,14 +1034,8 @@ void Item_sum_count::clear()
 
 bool Item_sum_count::add()
 {
-  if (!args[0]->maybe_null)
+  if (!args[0]->maybe_null || !args[0]->is_null())
     count++;
-  else
-  {
-    (void) args[0]->val_int();
-    if (!args[0]->null_value)
-      count++;
-  }
   return 0;
 }
 
@@ -1941,14 +1935,8 @@ void Item_sum_count::reset_field()
   char *res=result_field->ptr;
   longlong nr=0;
 
-  if (!args[0]->maybe_null)
+  if (!args[0]->maybe_null || !args[0]->is_null())
     nr=1;
-  else
-  {
-    (void) args[0]->val_int();
-    if (!args[0]->null_value)
-      nr=1;
-  }
   int8store(res,nr);
 }
 
@@ -2051,14 +2039,8 @@ void Item_sum_count::update_field()
   char *res=result_field->ptr;
 
   nr=sint8korr(res);
-  if (!args[0]->maybe_null)
+  if (!args[0]->maybe_null || !args[0]->is_null())
     nr++;
-  else
-  {
-    (void) args[0]->val_int();
-    if (!args[0]->null_value)
-      nr++;
-  }
   int8store(res,nr);
 }
 
@@ -2531,12 +2513,8 @@ bool Item_sum_count_distinct::setup(THD *thd)
     Item *item=args[i];
     if (list.push_back(item))
       return TRUE;                              // End of memory
-    if (item->const_item())
-    {
-      (void) item->val_int();
-      if (item->null_value)
-	always_null=1;
-    }
+    if (item->const_item() && item->is_null())
+      always_null= 1;
   }
   if (always_null)
     return FALSE;