BUG#834739: Wrong result with 3-way inner join, LooseScan,multipart keys

- Don't use join buffering for tables that are within ranges that are 
  covered by LooseScan strategy.

3 files changed, 15 insertions, 0 deletions

diff --git a/sql/opt_subselect.cc b/sql/opt_subselect.cc
index 40a0195e554..9ea55390fc5 100644
--- a/sql/opt_subselect.cc
+++ b/sql/opt_subselect.cc
@@ -3827,6 +3827,8 @@ int setup_semijoin_dups_elimination(JOIN *join, ulonglong options,
       {
         /* We jump from the last table to the first one */
         tab->loosescan_match_tab= tab + pos->n_sj_tables - 1;
+        for (uint j= i; j < pos->n_sj_tables; j++)
+          join->join_tab[j].inside_loosescan_range= TRUE;
 
         /* Calculate key length */
         keylen= 0;
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index 9aab58c1742..6ddb350db1d 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -7100,6 +7100,7 @@ get_best_combination(JOIN *join)
       goto loop_end;					// Handled in make_join_stat..
 
     j->loosescan_match_tab= NULL;  //non-nulls will be set later
+    j->inside_loosescan_range= FALSE;
     j->ref.key = -1;
     j->ref.key_parts=0;
 
@@ -8984,6 +8985,15 @@ uint check_join_cache_usage(JOIN_TAB *tab,
 
   if (tab->use_quick == 2)
     goto no_join_cache;
+  
+  /*
+    Don't use join cache if we're inside a join tab range covered by LooseScan
+    strategy (TODO: LooseScan is very similar to FirstMatch so theoretically it 
+    should be possible to use join buffering in the same way we're using it for
+    multi-table firstmatch ranges).
+  */
+  if (tab->inside_loosescan_range)
+    goto no_join_cache;
 
   if (tab->is_inner_table_of_semi_join_with_first_match() &&
       !join->allowed_semijoin_with_cache)
diff --git a/sql/sql_select.h b/sql/sql_select.h
index 9b53c53f690..15711dca7b3 100644
--- a/sql/sql_select.h
+++ b/sql/sql_select.h
@@ -347,6 +347,9 @@ typedef struct st_join_table {
      NULL - Not doing a loose scan on this join tab.
   */
   struct st_join_table *loosescan_match_tab;
+  
+  /* TRUE <=> we are inside LooseScan range */
+  bool inside_loosescan_range;
 
   /* Buffer to save index tuple to be able to skip duplicates */
   uchar *loosescan_buf;