php - 請問這多表聯查的SQL怎麼寫?

Question

我的問題如下圖所述,資料庫結構及資料在下面程式碼區塊,求大牛幫忙看看..

我希望得到的結果是:

表結構及資料如下

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');

這麼可以滿足我的需求,但是執行效率太低了...

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 ;

有沒有大牛能提供一個更有效率的寫法呢?

Answer 1

雷雷

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

如果是上面的資料的話，這條sql應該就滿足了。 。 。在不滿足，就不管了......

這是我的查詢結果

Answer 3

雷雷

Answer 4

你想要什麼，問題都沒有描述清楚。 。 。

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 ;

效率有問題..