In most cases you should use GRANT to set up your users/passwords, so the following only applies for advanced users. See GRANT.
The examples in the preceding sections illustrate an important principle: when you store a non-empty password using INSERT or UPDATE statements, you must use the PASSWORD() function to encrypt it. This is because the user table stores passwords in encrypted form, not as plaintext. If you forget that fact, you are likely to attempt to set passwords like this:
shell> mysql -u root mysql mysql> INSERT INTO user (Host,User,Password) -> VALUES('%','jeffrey','biscuit'); mysql> FLUSH PRIVILEGES;
The result is that the plaintext value 'biscuit' is stored as the password in the user table. When the user jeffrey attempts to connect to the server using this password, the mysql client encrypts it with PASSWORD(), generates an authentication vector based on encrypted password and a random number, obtained from server, and sends the result to the server. The server uses the password value in the user table (that is not encrypted value 'biscuit') to perform the same calculations, and compares results. The comparison fails and the server rejects the connection:
shell> mysql -u jeffrey -pbiscuit test Access denied
Passwords must be encrypted when they are inserted in the user table, so the INSERT statement should have been specified like this instead:
mysql> INSERT INTO user (Host,User,Password) -> VALUES('%','jeffrey',PASSWORD('biscuit'));
You must also use the PASSWORD() function when you use SET PASSWORD statements:
mysql> SET PASSWORD FOR jeffrey@"%" = PASSWORD('biscuit');
If you set passwords using the GRANT ... IDENTIFIED BY statement or the mysqladmin password command, the PASSWORD() function is unnecessary. They both take care of encrypting the password for you, so you would specify a password of 'biscuit' like this:
mysql> GRANT USAGE ON *.* TO jeffrey@"%" IDENTIFIED BY 'biscuit';
or:
shell> mysqladmin -u jeffrey password biscuit
Note: PASSWORD() is different from Unix password encryption. See User names.