item.cc:

  After review fix


sql/item.cc:
  After review fix

sql/item.cc

@@ -455,16 +455,18 @@ bool DTCollation::aggregate(DTCollation &dt, uint flags)
        ; // Do nothing
     }
     else if ((flags & MY_COLL_ALLOW_SUPERSET_CONV) &&
-             derivation <= dt.derivation &&
              collation->state & MY_CS_UNICODE &&
-             !(dt.collation->state & MY_CS_UNICODE))
+             (derivation < dt.derivation ||
+             (derivation == dt.derivation &&
+             !(dt.collation->state & MY_CS_UNICODE))))
     {
       // Do nothing
     }
     else if ((flags & MY_COLL_ALLOW_SUPERSET_CONV) &&
-             dt.derivation <= derivation &&
              dt.collation->state & MY_CS_UNICODE &&
-             !(collation->state & MY_CS_UNICODE))
+             (dt.derivation < derivation ||
+              (dt.derivation == derivation &&
+             !(collation->state & MY_CS_UNICODE))))
     {
       set(dt);
     }