Add 5.0 part of fix for bug 17047.

mysql-test/r/func_str.result:
  Add result for bug#17047: CHAR() and IN() can return NULL without
  signaling NULL result.
mysql-test/t/func_str.test:
  Add test case for bug#17047: CHAR() and IN() can return NULL without
  signaling NULL result.
sql/item_strfunc.cc:
  Add Item_str_func::fix_fields() implementation, and set maybe_null to
  TRUE if we are in the SQL mode that requires some functions to return
  null even if they normally do not.
sql/item_strfunc.h:
  Add declaration of Item_str_func::fix_fields().
  Do not reset maybe_null in Item_func_char::fix_length_and_dec().

1 files changed, 14 insertions, 0 deletions

diff --git a/sql/item_strfunc.cc b/sql/item_strfunc.cc
index 31c2f44fc3e..b54f8fef90c 100644
--- a/sql/item_strfunc.cc
+++ b/sql/item_strfunc.cc
@@ -80,6 +80,20 @@ String *Item_str_func::check_well_formed_result(String *str)
 }
 
 
+bool Item_str_func::fix_fields(THD *thd, Item **ref)
+{
+  bool res= Item_func::fix_fields(thd, ref);
+  /*
+    In Item_str_func::check_well_formed_result() we may set null_value
+    flag on the same condition as in test() below.
+  */
+  maybe_null= (maybe_null ||
+               test(thd->variables.sql_mode &
+                    (MODE_STRICT_TRANS_TABLES | MODE_STRICT_ALL_TABLES)));
+  return res;
+}
+
+
 my_decimal *Item_str_func::val_decimal(my_decimal *decimal_value)
 {
   DBUG_ASSERT(fixed == 1);