Manual merge

mysql-test/r/func_gconcat.result:
  Auto merged
mysql-test/t/func_gconcat.test:
  Auto merged

mysql-test/r/func_gconcat.result

@@ -576,3 +576,23 @@ group_concat('x')
 NULL
 1
 drop table t1;
+CREATE TABLE t1 (id int, a varchar(9));
+INSERT INTO t1 VALUES
+(2, ''), (1, ''), (2, 'x'), (1, 'y'), (3, 'z'), (3, '');
+SELECT GROUP_CONCAT(a) FROM t1;
+GROUP_CONCAT(a)
+,,x,y,z,
+SELECT GROUP_CONCAT(a ORDER BY a) FROM t1;
+GROUP_CONCAT(a ORDER BY a)
+,,,x,y,z
+SELECT GROUP_CONCAT(a) FROM t1 GROUP BY id;
+GROUP_CONCAT(a)
+,y
+,x
+z,
+SELECT GROUP_CONCAT(a ORDER BY a) FROM t1 GROUP BY id;
+GROUP_CONCAT(a ORDER BY a)
+,y
+,x
+,z
+DROP TABLE t1;

mysql-test/t/func_gconcat.test

@@ -373,4 +373,20 @@ select * from (select group_concat(a) from t1) t2;
 select group_concat('x') UNION ALL select 1;
 drop table t1;
 
+#
+# Bug #12863 : missing separators after first empty cancatanated elements
+#
+
+CREATE TABLE t1 (id int, a varchar(9));
+INSERT INTO t1 VALUES
+  (2, ''), (1, ''), (2, 'x'), (1, 'y'), (3, 'z'), (3, '');
+
+SELECT GROUP_CONCAT(a) FROM t1;
+SELECT GROUP_CONCAT(a ORDER BY a) FROM t1;
+
+SELECT GROUP_CONCAT(a) FROM t1 GROUP BY id;
+SELECT GROUP_CONCAT(a ORDER BY a) FROM t1 GROUP BY id;
+
+DROP TABLE t1;
+
 # End of 4.1 tests

sql/item_sum.cc

@@ -2740,8 +2740,10 @@ int dump_leaf_key(byte* key, element_count count __attribute__((unused)),
   String *result= &item->result;
   Item **arg= item->args, **arg_end= item->args + item->arg_count_field;
 
-  if (result->length())
-    result->append(*item->separator);
+  if (item->no_appended)
+    item->no_appended= FALSE;
+  else
+    item->result.append(*item->separator);
 
   tmp.length(0);
 
@@ -2925,6 +2927,7 @@ void Item_func_group_concat::clear()
   result.copy();
   null_value= TRUE;
   warning_for_row= FALSE;
+  no_appended= TRUE;
   if (tree)
     reset_tree(tree);
   /* No need to reset the table as we never call write_row */
@@ -2969,6 +2972,12 @@ bool Item_func_group_concat::add()
 }
 
 
+void Item_func_group_concat::reset_field()
+{
+  DBUG_ASSERT(0);
+}
+
+
 bool
 Item_func_group_concat::fix_fields(THD *thd, Item **ref)
 {