高性能MySQL（三）：服务器性能剖析

select * from c LEFT JOIN c100w on c.id=c100w.id;  -- 联合查询
show PROFILES;  -- 查看查询耗时
select * from c;
show PROFILE for  query 1 ;

set @query_id=282;
select state,sum(DURATION) as total_r,
ROUND(100*sum(duration)/(select sum(duration) from information_schema.PROFILING 
where QUERY_ID=@query_id),2) as pct_r,
count(*) as calls,
sum(duration)/count(*) as "r/call"
from information_schema.PROFILING
where QUERY_ID=@query_id
GROUP BY STATE
order by total_r desc

查询优化