Fix for bug#19667 group by a decimal expression yields wrong result

mysql-test/r/type_newdecimal.result:
  Fix for bug#19667 group by a decimal expression yields wrong result
   test case
mysql-test/t/type_newdecimal.test:
  Fix for bug#19667 group by a decimal expression yields wrong result
   test case

mysql-test/r/type_newdecimal.result

@@ -1397,3 +1397,14 @@ c1
 9999999999999999999999999999999999999999999999999999999999999999
 9999999999999999999999999999999999999999999999999999999999999999
 drop table t1;
+create table t1 (i int, j int);
+insert into t1 values (1,1), (1,2), (2,3), (2,4);
+select i, count(distinct j) from t1 group by i;
+i	count(distinct j)
+1	2
+2	2
+select i+0.0 as i2, count(distinct j) from t1 group by i2;
+i2	count(distinct j)
+1.0	2
+2.0	2
+drop table t1;

mysql-test/t/type_newdecimal.test

@@ -1095,3 +1095,12 @@ insert into t1 values(
 insert into t1 values(1e100);
 select * from t1;
 drop table t1;
+
+#
+# Bug#19667 group by a decimal expression yields wrong result
+#
+create table t1 (i int, j int);
+insert into t1 values (1,1), (1,2), (2,3), (2,4);
+select i, count(distinct j) from t1 group by i;
+select i+0.0 as i2, count(distinct j) from t1 group by i2;
+drop table t1;

sql/item_buff.cc

@@ -132,7 +132,7 @@ bool Cached_item_decimal::cmp()
 {
   my_decimal tmp;
   my_decimal *ptmp= item->val_decimal(&tmp);
-  if (null_value != item->null_value || my_decimal_cmp(&value, ptmp) == 0)
+  if (null_value != item->null_value || my_decimal_cmp(&value, ptmp))
   {
     null_value= item->null_value;
     my_decimal2decimal(ptmp, &value);