Bug#30245: A wrong type of a BIT field is reported when grouped by it.

HEAP tables can't index BIT fields. Due to this when grouping by such fields is
needed they are converted to a fields of the LONG type when temporary table
is being created. But a side effect of this is that a wrong type of BIT
fields is returned to a client.

Now the JOIN::prepare and the create_distinct_group functions are create
additional hidden copy of BIT fields to preserve original fields untouched.
New hidden fields are used for grouping instead.

mysql-test/r/type_bit.result

@@ -642,4 +642,19 @@ b+0	COUNT(DISTINCT a)
 1	1
 3	2
 DROP TABLE t1;
+CREATE TABLE t1 (b BIT);
+INSERT INTO t1 (b) VALUES (1), (0);
+SELECT DISTINCT b FROM t1;
+Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
+def	test	t1	t1	b	b	16	1	1	Y	32	0	63
+b
+#
+#
+SELECT b FROM t1 GROUP BY b;
+Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
+def	test	t1	t1	b	b	16	1	1	Y	32	0	63
+b
+#
+#
+DROP TABLE t1;
 End of 5.0 tests

mysql-test/t/type_bit.test

@@ -291,4 +291,17 @@ INSERT INTO t1 (b, a) VALUES (1, 1), (3, 2), (0, 3), (3, 4);
 SELECT b+0, COUNT(DISTINCT a) FROM t1 GROUP BY b;
 DROP TABLE t1;
 
+#
+# Bug#30245: A wrong type of a BIT field is reported when grouped by it.
+#
+CREATE TABLE t1 (b BIT);
+INSERT INTO t1 (b) VALUES (1), (0);
+--enable_metadata
+--replace_column 1 #
+SELECT DISTINCT b FROM t1;
+--replace_column 1 #
+SELECT b FROM t1 GROUP BY b;
+--disable_metadata
+DROP TABLE t1;
+
 --echo End of 5.0 tests

sql/sql_select.cc

@@ -189,6 +189,7 @@ static bool setup_new_fields(THD *thd, List<Item> &fields,
 			     List<Item> &all_fields, ORDER *new_order);
 static ORDER *create_distinct_group(THD *thd, Item **ref_pointer_array,
                                     ORDER *order, List<Item> &fields,
+                                    List<Item> &all_fields,
 				    bool *all_order_by_fields_used);
 static bool test_if_subpart(ORDER *a,ORDER *b);
 static TABLE *get_sort_by_table(ORDER *a,ORDER *b,TABLE_LIST *tables);
@@ -537,6 +538,28 @@ JOIN::prepare(Item ***rref_pointer_array,
       fix_inner_refs(thd, all_fields, select_lex, ref_pointer_array))
     DBUG_RETURN(-1);
 
+  if (group)
+  {
+    /*
+      Because HEAP tables can't index BIT fields we need to use an
+      additional hidden field for grouping because later it will be
+      converted to a LONG field. Original field will remain of the
+      BIT type and will be returned to a client.
+    */
+    for (ORDER *ord= group_list; ord; ord= ord->next)
+    {
+      if ((*ord->item)->type() == Item::FIELD_ITEM &&
+          (*ord->item)->field_type() == MYSQL_TYPE_BIT)
+      {
+        Item_field *field= new Item_field(thd, *(Item_field**)ord->item);
+        int el= all_fields.elements;
+        ref_pointer_array[el]= field;
+        all_fields.push_front(field);
+        ord->item= ref_pointer_array + el;
+      }
+    }
+  }
+
   if (setup_ftfuncs(select_lex)) /* should be after having->fix_fields */
     DBUG_RETURN(-1);
   
@@ -1068,12 +1091,13 @@ JOIN::optimize()
     if (order)
       skip_sort_order= test_if_skip_sort_order(tab, order, select_limit, 1);
     if ((group_list=create_distinct_group(thd, select_lex->ref_pointer_array,
-                                          order, fields_list,
+                                          order, fields_list, all_fields,
 				          &all_order_fields_used)))
     {
       bool skip_group= (skip_sort_order &&
 			test_if_skip_sort_order(tab, group_list, select_limit,
 						1) != 0);
+      count_field_types(select_lex, &tmp_table_param, all_fields, 0);
       if ((skip_group && all_order_fields_used) ||
 	  select_limit == HA_POS_ERROR ||
 	  (order && !skip_sort_order))
@@ -13647,10 +13671,11 @@ setup_new_fields(THD *thd, List<Item> &fields,
 static ORDER *
 create_distinct_group(THD *thd, Item **ref_pointer_array,
                       ORDER *order_list, List<Item> &fields,
+                      List<Item> &all_fields,
 		      bool *all_order_by_fields_used)
 {
   List_iterator<Item> li(fields);
-  Item *item;
+  Item *item, **orig_ref_pointer_array= ref_pointer_array;
   ORDER *order,*group,**prev;
 
   *all_order_by_fields_used= 1;
@@ -13690,12 +13715,31 @@ create_distinct_group(THD *thd, Item **ref_pointer_array,
       ORDER *ord=(ORDER*) thd->calloc(sizeof(ORDER));
       if (!ord)
 	return 0;
+
+      if (item->type() == Item::FIELD_ITEM &&
+          item->field_type() == MYSQL_TYPE_BIT)
+      {
+        /*
+          Because HEAP tables can't index BIT fields we need to use an
+          additional hidden field for grouping because later it will be
+          converted to a LONG field. Original field will remain of the
+          BIT type and will be returned to a client.
+        */
+        Item_field *new_item= new Item_field(thd, (Item_field*)item);
+        int el= all_fields.elements;
+        orig_ref_pointer_array[el]= new_item;
+        all_fields.push_front(new_item);
+        ord->item= orig_ref_pointer_array + el;
+      }
+      else
+      {
         /*
           We have here only field_list (not all_field_list), so we can use
           simple indexing of ref_pointer_array (order in the array and in the
           list are same)
         */
         ord->item= ref_pointer_array;
+      }
       ord->asc=1;
       *prev=ord;
       prev= &ord->next;