BUG#15024: get_best_covering_ror_intersect() tries to build ROR-intersection

by starting with an empty index set and adding indexes to it until it
becomes covering. If the set becomes covering after adding the first index,
return NULL and don't try constructing ROR-intersection of one index (which
caused a crash)

1 files changed, 4 insertions, 4 deletions

diff --git a/sql/opt_range.cc b/sql/opt_range.cc
index 323e829f219..bf7eb370e42 100644
--- a/sql/opt_range.cc
+++ b/sql/opt_range.cc
@@ -3136,10 +3136,10 @@ TRP_ROR_INTERSECT *get_best_covering_ror_intersect(PARAM *param,
     /* F=F-covered by first(I) */
     bitmap_union(&covered_fields, &(*ror_scan_mark)->covered_fields);
     all_covered= bitmap_is_subset(&param->needed_fields, &covered_fields);
-  } while (!all_covered && (++ror_scan_mark < ror_scans_end));
-
-  if (!all_covered)
-    DBUG_RETURN(NULL); /* should not happen actually */
+  } while ((++ror_scan_mark < ror_scans_end) && !all_covered);
+  
+  if (!all_covered || (ror_scan_mark - tree->ror_scans) == 1)
+    DBUG_RETURN(NULL);
 
   /*
     Ok, [tree->ror_scans .. ror_scan) holds covering index_intersection with