1，查看所有数据库大小
use information_schema;
select concat(round(sum(DATA_LENGTH/1024/1024),2),'MB') as data from TABLES;
2，查看指定数据库大小
use information_schema;
select concat(round(sum(DATA_LENGTH/1024/1024),2),'MB') as data from TABLES where table_schema='dbname';
3，查看指定数据库中指定表的大小
use information_schema;
select concat(round(sum(data_length/1024/1024),2),'MB') as data from tables where table_schema='dbname' and table_name='tbname';
4，查看日志文件位置
show variables like 'general_log_file'; 日志文件路径
show variables like 'log_error'; 错误日志文件路径
show variables like 'slow_query_log_file'; 慢查询日志文件路径
5，查询重复数据
select user ,count(user) as count from dz_wx_users GROUP BY user HAVING count(user) >1
select * from dz_wx_users where user in (select user from dz_wx_users GROUP BY user HAVING count(user) >1)