fixed collation of Item_cache family (BUG#951)

mysql-test/r/subselect.result:
  test of collation
mysql-test/t/subselect.test:
  test of collation
sql/item.cc:
  coping collation in the cache
sql/item.h:
  coping collation in the cache

mysql-test/r/subselect.result

@@ -1251,3 +1251,10 @@ a
 2
 10
 drop table t1,t2;
+CREATE TABLE t1 (s1 CHAR(5) COLLATE latin1_german1_ci,
+s2 CHAR(5) COLLATE latin1_swedish_ci);
+INSERT INTO t1 VALUES ('z','?');
+select * from t1 where s1 > (select max(s2) from t1);
+ERROR HY000: Illegal mix of collations (latin1_german1_ci,IMPLICIT) and (latin1_swedish_ci,IMPLICIT) for operation '>'
+select * from t1 where s1 > any (select max(s2) from t1);
+drop table t1;

mysql-test/t/subselect.test

@@ -853,3 +853,14 @@ insert into t3 values (1),(2),(10),(50);
 select a from t3 where t3.a in (select a from t1 where a <= 3 union select * from t2 where a <= 30);
 drop table t1,t2;
 
+#
+# collation test
+#
+CREATE TABLE t1 (s1 CHAR(5) COLLATE latin1_german1_ci,
+                 s2 CHAR(5) COLLATE latin1_swedish_ci);
+INSERT INTO t1 VALUES ('z','?');
+-- error 1265
+select * from t1 where s1 > (select max(s2) from t1);
+-- error 1265
+select * from t1 where s1 > any (select max(s2) from t1);
+drop table t1;

sql/item.cc

@@ -1704,7 +1704,7 @@ void Item_cache_str::store(Item *item)
     str_value.copy(*value);
     value= &str_value;
   }
-
+  collation.set(item->collation);
 }
 double Item_cache_str::val()
 { 

sql/item.h

@@ -852,6 +852,7 @@ public:
   {
     value= item->val_int_result();
     null_value= item->null_value;
+    collation.set(item->collation);
   }
   double val() { return (double) value; }
   longlong val_int() { return value; }
@@ -869,6 +870,7 @@ public:
   {
     value= item->val_result();
     null_value= item->null_value;
+    collation.set(item->collation);
   }
   double val() { return value; }
   longlong val_int() { return (longlong) (value+(value > 0 ? 0.5 : -0.5)); }