Fixed bug#20825: rollup puts non-equal values together

Fix for bug 7894 replaces a field(s) in a non-aggregate function with a item
reference if such a field was specified in the GROUP BY clause in order to
get a correct result.
When ROLLUP is involved this lead to a wrong result due to value of a such
field is got through a copy function and copying happens after the function
evaluation.
Such replacement isn't needed if grouping is also done by such a function.

The change_group_ref() function now isn't called for a function present in
the group list.

mysql-test/r/olap.result

@@ -541,3 +541,18 @@ a	max(b)
 NULL	2
 a	1
 drop table t1;
+create table t1 (a varchar(22) not null , b int);
+insert into t1 values ("2006-07-01 21:30", 1), ("2006-07-01 23:30", 10);
+select left(a,10), a, sum(b) from t1 group by 1,2 with rollup;
+left(a,10)	a	sum(b)
+2006-07-01	2006-07-01 21:30	1
+2006-07-01	2006-07-01 23:30	10
+2006-07-01	NULL	11
+NULL	NULL	11
+select left(a,10) x, a, sum(b) from t1 group by x,a with rollup;
+x	a	sum(b)
+2006-07-01	2006-07-01 21:30	1
+2006-07-01	2006-07-01 23:30	10
+2006-07-01	NULL	11
+NULL	NULL	11
+drop table t1;

mysql-test/t/olap.test

@@ -272,4 +272,13 @@ select a, max(b) from t1 group by a with rollup;
 select distinct a, max(b) from t1 group by a with rollup;
 drop table t1;
 
+#
+# Bug #20825: rollup puts non-equal values together
+#
+create table t1 (a varchar(22) not null , b int);
+insert into t1 values ("2006-07-01 21:30", 1), ("2006-07-01 23:30", 10);
+select left(a,10), a, sum(b) from t1 group by 1,2 with rollup;
+select left(a,10) x, a, sum(b) from t1 group by x,a with rollup;
+drop table t1;
+
 # End of 4.1 tests

sql/sql_select.cc

@@ -9706,12 +9706,17 @@ bool JOIN::rollup_init()
   while ((item= it++))
   {
     ORDER *group_tmp;
+    bool found_in_group= 0;
+
     for (group_tmp= group_list; group_tmp; group_tmp= group_tmp->next)
     {
       if (*group_tmp->item == item)
+      {
         item->maybe_null= 1;
+        found_in_group= 1;
+      }
     }
-    if (item->type() == Item::FUNC_ITEM)
+    if (item->type() == Item::FUNC_ITEM && !found_in_group)
     {
       bool changed= FALSE;
       if (change_group_ref(thd, (Item_func *) item, group_list, &changed))