php - How to write the SQL for this multi-table joint query?

Question

My problem is as shown in the picture below. The database structure and data are in the code block below. Please help me.

< /p>

The result I hope to get is:

The table structure and data are as follows

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');

This can meet my needs, but the execution efficiency is too low...

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 ;

Is there any expert who can provide a more efficient way of writing?

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..