php - 请问这条多表联查的SQL怎么写?
我的问题如下图所述,数据库结构及数据在下面代码块,求大牛帮忙看看..
我希望得到的结果是:
表结构及数据如下
CREATE TABLE A(
id INT NOT NULL,
num INT NOT NULL
)CHARSET=utf8;
INSERT INTO A(id,num) VALUES(1,5),(2,7),(3,6);
CREATE TABLE B(
aid INT NOT NULL,
sid INT NOT NULL,
content VARCHAR(20) NOT NULL
)CHARSET=utf8;
INSERT INTO B(aid,sid,content) VALUES(3,1,'A'),(3,2,'B'),(3,3,'C');
CREATE TABLE C(
id INT NOT NULL,
time INT NOT NULL,
libs VARCHAR(20) NOT NULL
)CHARSET=utf8;
INSERT INTO C(id,time,libs) VALUES(2,18,'wagaga'),(3,16,'aaaa'),(1,15,'cc'),(3,17,'dddd'),(4,14,'eeee'),(3,10,'ffff'),(3,11,'bbbb');这么可以满足我的需求,但是执行效率太低了...
select * from
(
SELECT distinct
a.id,a.num,b.aid,b.sid,b.content,c.id as cid,c.time,c.libs
FROM
a a
LEFT JOIN b b ON b.aid = a.id
LEFT JOIN c ON c.id = b.sid
WHERE a.id = 3
ORDER BY time DESC
) as TMP
GROUP BY cid ;有没有大牛能提供一个更效率的写法呢?
