Retrieve Specific Data/Value From Database 1 Line PHP

I'm just wondering how I can retrieve a specific value (only 1 thing will be returned) from a database using php.

My query is

mysql_query(开发者_StackOverflow中文版"SELECT balance FROM users WHERE username = '". $this->username . "'")

I'm just looking for it to retrieve the data from that row so I can save it directory into a variable.

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In MySQL, you can limit the number of results using LIMIT:

mysql_query("SELECT balance FROM users WHERE username = '". $this->username . "' LIMIT 1")