fix for a bug in CASE ...WHEN ...

mysql-test/r/case.result

@@ -40,3 +40,7 @@ fcase	count(*)
 nothing	2
 one	1
 two	1
+color
+orange
+yellow
+green

mysql-test/t/case.test

@@ -30,3 +30,8 @@ insert into t1 values(1),(2),(3),(4);
 select case a when 1 then 2 when 2 then 3 else 0 end as fcase, count(*) from t1 group by fcase;
 select case a when 1 then "one" when 2 then "two" else "nothing" end as fcase, count(*) from t1 group by fcase;
 drop table t1;
+drop table if exists t;
+create table t1 (row int not null, col int not null, val varchar(255) not null);
+insert into t1 values (1,1,'orange'),(1,2,'large'),(2,1,'yellow'),(2,2,'medium'),(3,1,'green'),(3,2,'small');
+select max(case col when 1 then val else null end) as color from t1 group by row;
+drop table if exists t;

sql/item_cmpfunc.cc

@@ -687,6 +687,8 @@ String *Item_func_case::val_str(String *str)
   }
   if (!(res=item->val_str(str)))
     null_value=1;
+  else
+    null_value=item->null_value;
   return res;
 }
 

sql/sql_db.cc

@@ -371,8 +371,6 @@ bool mysql_change_db(THD *thd,const char *name)
   }
   send_ok(&thd->net);
   x_free(thd->db);
-  if (lower_case_table_names)
-    casedn_str(dbname);
   thd->db=dbname;
   thd->db_access=db_access;
   DBUG_RETURN(0);