Fix and testcase for BUG#6699

myisam/mi_rnext_same.c:
  Fix for BUG#6699: 
    MERGE handler now uses mi_rnext_same() with priority queue, so skip record unpacking if buf==NULL
myisammrg/myrg_rnext_same.c:
  Fix for BUG#6699: 
   make myrg_rnext_same sort always sort records and return them in key order.
mysql-test/r/merge.result:
  Test for BUG#6699
mysql-test/t/merge.test:
  Test for BUG#6699

myisam/mi_rnext_same.c

@@ -88,6 +88,10 @@ int mi_rnext_same(MI_INFO *info, byte *buf)
     if (my_errno == HA_ERR_KEY_NOT_FOUND)
       my_errno=HA_ERR_END_OF_FILE;
   }
+  else if (!buf)
+  {
+    DBUG_RETURN(info->lastpos==HA_OFFSET_ERROR ? my_errno : 0);
+  }
   else if (!(*info->read_record)(info,info->lastpos,buf))
   {
     info->update|= HA_STATE_AKTIV;		/* Record is read */

myisammrg/myrg_rnext_same.c

@@ -16,25 +16,36 @@
 
 #include "myrg_def.h"
 
+
 int myrg_rnext_same(MYRG_INFO *info, byte *buf)
 {
-  uint err;
+  int err;
   MI_INFO *mi;
 
   if (!info->current_table)
     return (HA_ERR_KEY_NOT_FOUND);
 
-  err=mi_rnext_same(info->current_table->table,buf);
-  if (err == HA_ERR_END_OF_FILE)
+  /* at first, do rnext for the table found before */
+  if ((err=mi_rnext_same(info->current_table->table,NULL)))
   {
-    queue_remove(&(info->by_key),0);
-    if (!info->by_key.elements)
-      return HA_ERR_END_OF_FILE;
-
-    mi=(info->current_table=(MYRG_TABLE *)queue_top(&(info->by_key)))->table;
-    mi->once_flags|= RRND_PRESERVE_LASTINX;
-    return mi_rrnd(mi,buf,mi->lastpos);
+    if (err == HA_ERR_END_OF_FILE)
+    {
+      queue_remove(&(info->by_key),0);
+      if (!info->by_key.elements)
+        return HA_ERR_END_OF_FILE;
+    }
+    else
+      return err;
   }
-  return err;
+  else
+  {
+    /* Found here, adding to queue */
+    queue_top(&(info->by_key))=(byte *)(info->current_table);
+    queue_replaced(&(info->by_key));
+  }
+
+  /* now, mymerge's read_next is as simple as one queue_top */
+  mi=(info->current_table=(MYRG_TABLE *)queue_top(&(info->by_key)))->table;
+  return _myrg_mi_read_record(mi,buf);
 }
 

mysql-test/r/merge.result

@@ -651,3 +651,28 @@ ERROR HY000: You can't specify target table 't1' for update in FROM clause
 create table t3 engine=merge union=(t1, t2) select * from t2;
 ERROR HY000: You can't specify target table 't2' for update in FROM clause
 drop table t1, t2;
+create table t1 (a int,b int,c int, index (a,b,c));
+create table t2 (a int,b int,c int, index (a,b,c));
+create table t3 (a int,b int,c int, index (a,b,c))
+engine=merge union=(t1 ,t2);
+insert into t1 (a,b,c) values (1,1,0),(1,2,0);
+insert into t2 (a,b,c) values (1,1,1),(1,2,1);
+explain select a,b,c from t3 force index (a) where a=1 order by a,b,c;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t3	ref	a	a	5	const	2	Using where; Using index
+select a,b,c from t3 force index (a) where a=1 order by a,b,c;
+a	b	c
+1	1	0
+1	1	1
+1	2	0
+1	2	1
+explain select a,b,c from t3 force index (a) where a=1 order by a desc, b desc, c desc;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t3	ref	a	a	5	const	2	Using where; Using index
+select a,b,c from t3 force index (a) where a=1 order by a desc, b desc, c desc;
+a	b	c
+1	2	1
+1	2	0
+1	1	1
+1	1	0
+drop table t1, t2, t3;

mysql-test/t/merge.test

@@ -285,3 +285,21 @@ create table t3 engine=merge union=(t1, t2) select * from t1;
 --error 1093
 create table t3 engine=merge union=(t1, t2) select * from t2;
 drop table t1, t2;
+
+# BUG#6699 : no sorting on 'ref' retrieval 
+create table t1 (a int,b int,c int, index (a,b,c));
+create table t2 (a int,b int,c int, index (a,b,c));
+create table t3 (a int,b int,c int, index (a,b,c))
+  engine=merge union=(t1 ,t2);
+insert into t1 (a,b,c) values (1,1,0),(1,2,0);
+insert into t2 (a,b,c) values (1,1,1),(1,2,1);
+
+explain select a,b,c from t3 force index (a) where a=1 order by a,b,c;
+select a,b,c from t3 force index (a) where a=1 order by a,b,c;
+
+# this actually wasn't affected:
+explain select a,b,c from t3 force index (a) where a=1 order by a desc, b desc, c desc;
+select a,b,c from t3 force index (a) where a=1 order by a desc, b desc, c desc;
+
+drop table t1, t2, t3;
+