Question

因此,我试图以同样的id子加入多个,每个桌子可能或不可能有这种id。

SELECT a.value, b.value, c.value, d.value FROM tbl_a a 
JOIN tbl_b b ON a.id=b.id 
JOIN tbl_c c ON a.id=c.id
JOIN tbl_d d on a.id=d.id
WHERE a.id=123

显然,这种情况之所以失败,是因为如果 t子 t不入,它就留下了一个空洞的结果,而加入者失败。

我曾尝试过各种左派,外派加入,无法工作。我也试图确定这两个条款如下:WHERE a.id=123 OR b.id=123 OR :, 但那是没有工作。

我尝试了一种模糊不清的主意,但这种定论使产出分立。

SELECT count(*), "a", IFNULL(a.value,0) FROM tbl_a a WHERE a.id=123
UNION
SELECT count(*), "b", IFNULL(b.value,0) FROM tbl_b b WHERE b.id=123
UNION
etc...

任何想法?

Answer 1

添加其他三个<代码>id 页: 1 WHERE 加入:OR,然后加入。

Answer 2

Another approach is to create a derived table containing your desired key and LEFT JOIN-ing to all the other tables:

SELECT a.value, b.value, c.value, d.value 
FROM ( select 123 as id ) as dummy
LEFT JOIN tbl_a a ON dummy.id=a.id
LEFT JOIN tbl_b b ON dummy.id=b.id 
LEFT JOIN tbl_c c ON dummy.id=c.id
LEFT JOIN tbl_d d ON dummy.id=d.id

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