php - 请问这条多表联查的SQL怎么写?

Question

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?

Answer 1

SELECT
    a.id,a.num,b.aid,b.sid,b.content,c.id,substring_index(group_concat(c.time order by c.time desc),',',1) ctime,substring_index(group_concat(c.libs order by c.time desc),',',1) clibs
FROM a
JOIN b ON b.aid = a.id
JOIN c ON c.id = b.sid
WHERE a.id = 3
GROUP BY c.id ;

Answer 2

SELECT
    *
FROM
    a a
LEFT JOIN b b ON b.aid = a.id
LEFT JOIN c ON c.id = b.sid
WHERE a.id = 3
GROUP BY c.id

If it is the above data, this sql should be satisfied. . . If you are not satisfied, just don’t care...

This is my query result

Answer 3

select A.num,b.content,c.time,c.libs from A left join B on A.id=B.id left join C on C.id = A.id order by C.time desc limit 0,1

Answer 4

What you want is not clearly described in the question. . .

Answer 5

select * from
(
SELECT distinct
    a.id,a.num,b.aid,b.sid,b.content,c.id as cid,c.time,c.libs
FROM
    a
LEFT JOIN 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 ;

There is a problem with efficiency..