1. select count(*) from Sys_Channel t , U_User u where u.u_user_id
in ( select ss.last_op_id from Sys_Channel ss where ss.supplierinfo_id='0') and t.supplierinfo_id='0';
2. select count(*) from sys_channel s left join u_user u on s.last_op_id=u.u_user_id where s.supplierinfo_id='0'
第一条和第二条查询出的结果一样,但执行时间相差很大,你有什么好办法增快查询速度吗?