func_group.test, func_group.result:

  Added a test case for bug #9210.
sql_select.cc:
  Fixed bug #9210.
  The function calc_group_buffer did not cover the case
  when the GROUP BY expression was decimal.
  Slightly optimized the other code.

mysql-test/r/func_group.result

@@ -888,3 +888,62 @@ SELECT COUNT(DISTINCT a) FROM t1;
 COUNT(DISTINCT a)
 2
 DROP TABLE t1;
+CREATE TABLE t1 (a int, b int, c int);
+INSERT INTO t1 (a, b, c) VALUES
+(1,1,1), (1,1,2), (1,1,3),
+(1,2,1), (1,2,2), (1,2,3),
+(1,3,1), (1,3,2), (1,3,3),
+(2,1,1), (2,1,2), (2,1,3),
+(2,2,1), (2,2,2), (2,2,3),
+(2,3,1), (2,3,2), (2,3,3),
+(3,1,1), (3,1,2), (3,1,3),
+(3,2,1), (3,2,2), (3,2,3),
+(3,3,1), (3,3,2), (3,3,3);
+SELECT b/c as v, a FROM t1 ORDER BY v;
+v	a
+0.33333	3
+0.33333	1
+0.33333	2
+0.50000	1
+0.50000	2
+0.50000	3
+0.66667	2
+0.66667	1
+0.66667	3
+1.00000	3
+1.00000	2
+1.00000	3
+1.00000	1
+1.00000	2
+1.00000	3
+1.00000	2
+1.00000	1
+1.00000	1
+1.50000	3
+1.50000	2
+1.50000	1
+2.00000	1
+2.00000	3
+2.00000	2
+3.00000	3
+3.00000	2
+3.00000	1
+SELECT b/c as v, SUM(a) FROM t1 GROUP BY v;
+v	SUM(a)
+0.33333	6
+0.50000	6
+0.66667	6
+1.00000	18
+1.50000	6
+2.00000	6
+3.00000	6
+SELECT SUM(a) FROM t1 GROUP BY b/c;
+SUM(a)
+6
+6
+6
+18
+6
+6
+6
+DROP TABLE t1;

mysql-test/t/func_group.test

@@ -601,3 +601,26 @@ INSERT INTO t1 (a) VALUES ("A"), ("a"), ("a "), ("a   "),
                           ("B"), ("b"), ("b "), ("b   ");
 SELECT COUNT(DISTINCT a) FROM t1;
 DROP TABLE t1;
+
+#
+# Test for buf #9210: GROUP BY with expression if a decimal type
+#
+
+CREATE TABLE t1 (a int, b int, c int);
+INSERT INTO t1 (a, b, c) VALUES
+  (1,1,1), (1,1,2), (1,1,3),
+  (1,2,1), (1,2,2), (1,2,3),
+  (1,3,1), (1,3,2), (1,3,3),
+  (2,1,1), (2,1,2), (2,1,3),
+  (2,2,1), (2,2,2), (2,2,3),
+  (2,3,1), (2,3,2), (2,3,3),
+  (3,1,1), (3,1,2), (3,1,3),
+  (3,2,1), (3,2,2), (3,2,3),
+  (3,3,1), (3,3,2), (3,3,3);
+
+SELECT b/c as v, a FROM t1 ORDER BY v;
+SELECT b/c as v, SUM(a) FROM t1 GROUP BY v;
+SELECT SUM(a) FROM t1 GROUP BY b/c;
+
+DROP TABLE t1;
+

sql/sql_select.cc

@@ -11891,7 +11891,8 @@ calc_group_buffer(JOIN *join,ORDER *group)
     join->group= 1;
   for (; group ; group=group->next)
   {
-    Field *field=(*group->item)->get_tmp_table_field();
+    Item *group_item= *group->item;
+    Field *field= group_item->get_tmp_table_field();
     if (field)
     {
       if (field->type() == FIELD_TYPE_BLOB)
@@ -11901,27 +11902,36 @@ calc_group_buffer(JOIN *join,ORDER *group)
       else
 	key_length+= field->pack_length();
     }
-    else if ((*group->item)->result_type() == REAL_RESULT)
-      key_length+=sizeof(double);
-    else if ((*group->item)->result_type() == INT_RESULT)
-      key_length+=sizeof(longlong);
-    else if ((*group->item)->result_type() == STRING_RESULT)
-    {
-      /*
-        Group strings are taken as varstrings and require an length field.
-        A field is not yet created by create_tmp_field()
-        and the sizes should match up.
-      */
-      key_length+= (*group->item)->max_length + HA_KEY_BLOB_LENGTH;
-    }
     else
-    {
-      /* This case should never be choosen */
-      DBUG_ASSERT(0);
-      join->thd->fatal_error();
+    { 
+      switch (group_item->result_type()) {
+      case REAL_RESULT:
+        key_length+= sizeof(double);
+        break;
+      case INT_RESULT:
+        key_length+= sizeof(longlong);
+        break;
+      case DECIMAL_RESULT:
+        key_length+= my_decimal_get_binary_size(group_item->max_length - 
+                                                (group_item->decimals ? 1 : 0),
+                                                group_item->decimals);
+        break;
+      case STRING_RESULT:
+        /*
+          Group strings are taken as varstrings and require an length field.
+          A field is not yet created by create_tmp_field()
+          and the sizes should match up.
+        */
+        key_length+= group_item->max_length + HA_KEY_BLOB_LENGTH;
+        break;
+      default:
+        /* This case should never be choosen */
+        DBUG_ASSERT(0);
+        join->thd->fatal_error();
+      }
     }
     parts++;
-    if ((*group->item)->maybe_null)
+    if (group_item->maybe_null)
       null_parts++;
   }
   join->tmp_table_param.group_length=key_length+null_parts;