grant.result, grant.test:

  fixing tests accordingly
item.cc:
  Bug #10892 user variables not auto cast for comparisons
  When mixing strings with different character sets,
  and coercibility is the same, we allow conversion
  if one character set is superset for other character set.

mysql-test/r/grant.result

@@ -440,3 +440,6 @@ insert into tables_priv values ('','test_db','mysqltest_1','test_table','test_gr
 flush privileges;
 delete from tables_priv where host = '' and user = 'mysqltest_1';
 flush privileges;
+set @user123="non-existent";
+select * from mysql.db where user=@user123;
+Host	Db	User	Select_priv	Insert_priv	Update_priv	Delete_priv	Create_priv	Drop_priv	Grant_priv	References_priv	Index_priv	Alter_priv	Create_tmp_table_priv	Lock_tables_priv

mysql-test/t/grant.test

@@ -402,4 +402,11 @@ 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

@@ -455,14 +455,16 @@ 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)
+             derivation <= dt.derivation &&
+             collation->state & MY_CS_UNICODE &&
+             !(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.derivation <= derivation &&
+             dt.collation->state & MY_CS_UNICODE &&
+             !(collation->state & MY_CS_UNICODE))
     {
       set(dt);
     }