Question

Morning,

A little advice sought here.

Have a username column in a utf8-bin table.

Want to keep case sensitivity on usernames for login but wish to perform a case-insensitive check on availability of username.

what issues surround using

CONVERT(`usrnm` USING latin1) #or other charset.

when dealing with something like chinese or arabic?

Any tips/thoughts/comments most welcome.

Answer 1

CREATE TABLE users (id INT NOT NULL PRIMARY KEY, usrnm VARCHAR(20) COLLATE UTF8_BIN);

INSERT
INTO    users
VALUES  (1, 'Пользователь'); -- First letter in upper case

SELECT  *
FROM    users
WHERE   usrnm = 'пользователь'; -- First letter in lower case, not returned


SELECT  *
FROM    users
WHERE   usrnm COLLATE UTF8_GENERAL_CI = 'пользователь';  -- First letter in lower case, returned

Note that if you want to ensure case-insensitive uniqueness, it’s better to make the column UTF8_GENERAL_CI and declare it UNIQUE:

CREATE TABLE users (id INT NOT NULL PRIMARY KEY, usrnm VARCHAR(20) COLLATE UTF8_GENERAL_CI UNIQUE);

INSERT
INTO    users
VALUES  (1, 'Пользователь');

INSERT
INTO    users
VALUES  (2, 'пользователь'); -- unique violation

SELECT  *
FROM    users
WHERE   usrnm = 'пользователь' COLLATE UTF8_BIN;