BUG#30324: Grouping queries with COUNT(DISTINCT bit column) return wrong results

- The bug was caused by COUNT(DISTINCT ...) code using Unique object in 
  a way that assumed that BIT(N) column occupies a contiguous space in
  temp_table->record[0] buffer. 
- The fix is to make COUNT(DISTINCT ...) code instruct create_tmp_table to
  create temporary table with column of type BIGINT, not BIT(N).

mysql-test/r/type_bit.result

@@ -657,4 +657,19 @@ b
 #
 #
 DROP TABLE t1;
+CREATE TABLE t1 (a int, b bit(2));
+INSERT INTO t1 VALUES (3, 2), (2, 3), (2, 0), (3, 2), (3, 1);
+SELECT COUNT(DISTINCT b) FROM t1 GROUP BY a;
+COUNT(DISTINCT b)
+2
+2
+DROP TABLE t1;
+create table t2 (a int, b bit(2), c char(10));
+INSERT INTO t2 VALUES (3, 2, 'two'), (2, 3, 'three'), (2, 0, 'zero'), 
+(3, 2, 'two'), (3, 1, 'one');
+SELECT COUNT(DISTINCT b,c) FROM t2 GROUP BY a;
+COUNT(DISTINCT b,c)
+2
+2
+DROP TABLE t2;
 End of 5.0 tests

mysql-test/t/type_bit.test

@@ -304,4 +304,18 @@ SELECT b FROM t1 GROUP BY b;
 --disable_metadata
 DROP TABLE t1;
 
+#
+# BUG#30324 Wrong query result for COUNT(DISTINCT(bit_column))
+#
+CREATE TABLE t1 (a int, b bit(2));
+INSERT INTO t1 VALUES (3, 2), (2, 3), (2, 0), (3, 2), (3, 1);
+SELECT COUNT(DISTINCT b) FROM t1 GROUP BY a;
+DROP TABLE t1;
+
+create table t2 (a int, b bit(2), c char(10));
+INSERT INTO t2 VALUES (3, 2, 'two'), (2, 3, 'three'), (2, 0, 'zero'), 
+                      (3, 2, 'two'), (3, 1, 'one');
+SELECT COUNT(DISTINCT b,c) FROM t2 GROUP BY a;
+DROP TABLE t2;
+
 --echo End of 5.0 tests

sql/item_sum.cc

@@ -2464,6 +2464,23 @@ bool Item_sum_count_distinct::setup(THD *thd)
   count_field_types(select_lex, tmp_table_param, list, 0);
   tmp_table_param->force_copy_fields= force_copy_fields;
   DBUG_ASSERT(table == 0);
+  /*
+    Make create_tmp_table() convert BIT columns to BIGINT.
+    This is needed because BIT fields store parts of their data in table's
+    null bits, and we don't have methods to compare two table records, which
+    is needed by Unique which is used when HEAP table is used.
+  */
+  {
+    List_iterator_fast<Item> li(list);
+    Item *item;
+    while ((item= li++))
+    {
+      if (item->type() == Item::FIELD_ITEM &&
+          ((Item_field*)item)->field->type() == FIELD_TYPE_BIT)
+        item->marker=4;
+    }
+  }
+
   if (!(table= create_tmp_table(thd, tmp_table_param, list, (ORDER*) 0, 1,
 				0,
 				(select_lex->options | thd->options),