Hmm, why finding by '２' or '2' return the same record?

Question

forgive my newbie question, but why finding by '２' or '2' in Mysql returns the same record?

For example:

Say I have a record with string field named 'slug', and the value is '２'. And the following SQLs returns same record.

SELECT * From articles WHERE slug='2'  
SELECT * From articles WHERE slug='２' 

Answer 1

It has to do with the collation of your database:

mysql> SHOW VARIABLES LIKE 'collation_%';
+----------------------+-------------------+
| Variable_name        | Value             |
+----------------------+-------------------+
| collation_connection | latin1_swedish_ci |
| collation_database   | latin1_swedish_ci |
| collation_server     | latin1_swedish_ci |
+----------------------+-------------------+
3 rows in set (0.00 sec)

mysql> SELECT '２'='2';
+-----------+
| '２'='2' |
+-----------+
|         0 |
+-----------+
1 row in set (0.00 sec)

mysql> SET NAMES 'utf8' COLLATE 'utf8_unicode_ci';
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT '２'='2';
+-----------+
| '２'='2' |
+-----------+
|         1 |
+-----------+
1 row in set (0.00 sec)