Fixed bug #25798.

This bug may manifest itself not only with the queries for which
the index-merge access method is chosen. It also may display
itself for queries with DISTINCT.

The bug was in how the Unique::get method used the merge_buffers
function. To compare elements in the the queue employed by
merge_buffers() it must use the buffpek_compare function rather
than the function for binary comparison. 

1 files changed, 6 insertions, 7 deletions

diff --git a/sql/uniques.cc b/sql/uniques.cc
index 9eb827f62a3..7c197d2a2e9 100644
--- a/sql/uniques.cc
+++ b/sql/uniques.cc
@@ -361,17 +361,12 @@ Unique::reset()
 }
 
 /*
-  The comparison function, passed to queue_init() in merge_walk() must
+  The comparison function, passed to queue_init() in merge_walk() and in
+  merge_buffers() when the latter is called from Uniques::get() must
   use comparison function of Uniques::tree, but compare members of struct
   BUFFPEK.
 */
 
-struct BUFFPEK_COMPARE_CONTEXT
-{
-  qsort_cmp2 key_compare;
-  void *key_compare_arg;
-};
-
 C_MODE_START
 
 static int buffpek_compare(void *arg, byte *key_ptr1, byte *key_ptr2)
@@ -630,6 +625,10 @@ bool Unique::get(TABLE *table)
   sort_param.unique_buff= sort_buffer+(sort_param.keys*
 				       sort_param.sort_length);
 
+  sort_param.compare= (qsort2_cmp) buffpek_compare;
+  sort_param.cmp_context.key_compare= tree.compare;
+  sort_param.cmp_context.key_compare_arg= tree.custom_arg;
+
   /* Merge the buffers to one file, removing duplicates */
   if (merge_many_buff(&sort_param,sort_buffer,file_ptr,&maxbuffer,&file))
     goto err;