mysql数据库查询日志文件

如何用一条sql查询得到mysql的日志文件大小。。。。。。。。。。。。。。

 SELECT 
    table_name AS `Table`, 
    round(((data_length + index_length) / 1024 / 1024), 2) `Size in MB` 
FROM information_schema.TABLES 
WHERE table_schema = "$DB_NAME"
    AND table_name = "$TABLE_NAME";