Merge mysql.com:/usr/home/bar/mysql-4.1.b10892

into  mysql.com:/usr/home/bar/mysql-5.0

mysql-test/t/grant.test

@@ -480,4 +480,11 @@ flush privileges;
 delete from tables_priv where host = '' and user = 'mysqltest_1';
 flush privileges;
 
+#
+# Bug #10892 user variables not auto cast for comparisons
+# Check that we don't get illegal mix of collations
+#
+set @user123="non-existent";
+select * from mysql.db where user=@user123;
+
 # End of 4.1 tests

sql/item.cc

@@ -1016,14 +1016,18 @@ 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)
+             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)
+             dt.collation->state & MY_CS_UNICODE &&
+             (dt.derivation < derivation ||
+              (dt.derivation == derivation &&
+             !(collation->state & MY_CS_UNICODE))))
     {
       set(dt);
     }