I create a table with CHARSET=tis620 and insert two rows "เด็กน้อย" and "เด้กน้อย". Notice the difference in the third character. Then when I do selection on each word I just inserted, instead of returning only one row, it returns both rows for both selection. mysql> CREATE TABLE `test` ( -> `word` varchar(100) default NULL -> ) ENGINE=MyISAM DEFAULT CHARSET=tis620; Query OK, 0 rows affected (0.02 sec) mysql> INSERT INTO test (word) VALUES ('เด็กน้อย'); Query OK, 1 row affected (0.00 sec) mysql> INSERT INTO test (word) VALUES ('เด้กน้อย'); Query OK, 1 row affected (0.00 sec) mysql> select * from test where word='เด็กน้อย'; +----------+ | word | +----------+ | เด็กน้อย | | เด้กน้อย | +----------+ 2 rows in set (0.00 sec) mysql> select * from test where word='เด้กน้อย'; +----------+ | word | +----------+ | เด็กน้อย | | เด้กน้อย | +----------+ 2 rows in set (0.00 sec)