Fixed bug #36488: regexp returns false matches, concatenating

                  with previous rows.

The WHERE clause containing expression:
  CONCAT(empty_field1, empty_field2, ..., 'literal constant', ...)
    REGEXP 'regular expression'
may return wrong matches.

Optimization of the CONCAT function has been fixed.

1 files changed, 6 insertions, 0 deletions

diff --git a/sql/item_strfunc.cc b/sql/item_strfunc.cc
index 4e72f117869..c443364ce52 100644
--- a/sql/item_strfunc.cc
+++ b/sql/item_strfunc.cc
@@ -294,6 +294,12 @@ String *Item_func_concat::val_str(String *str)
     {
       if (!(res=args[i]->val_str(str)))
 	goto null;
+      /*
+       CONCAT accumulates its result in the result of its the first
+       non-empty argument. Because of this we need is_const to be 
+       evaluated only for it.
+      */
+      is_const= args[i]->const_item() || !args[i]->used_tables();
     }
     else
     {