desc 表 ta, tb:
create table ta (
id bigint primary key auto_increment,
name varchar(20) default ''
);
create table tb (
id bigint primary key auto_increment,
aid bigint references ta,
home varchar(20) default '',
index tb_aid (aid)
);
加载测试数据,ta的大小为400k,tb的大小为200k
sql 一个成本-时间 3s
select *
from ta left join tb on ta.id = tb.aid
order by ta.id desc, tb.id desc
limit 10
sql B 成本-时间 74ms(只需删除
, tb.id desc
):
select *
from ta left join tb on ta.id = tb.aid
order by ta.id desc
limit 10
如何提高sql A速度?