如何连接三张表

Question

我有三个表，其中两个在结构上相同

像这样的表 1

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id       title     description       image
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1         title1   desc1             image1.png
2         title2    desc2            image2.jpg
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像这样的表2

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id       title     description       image
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1         ttl1   des1             img1.png
2         ttl2    des2            img2.jpg
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表 3 是这样的

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id       table1_id    table2_id     
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1         0             1             
2         1             0    
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我想将 table3 连接到 id 不为零的其他表之一。

Answer 1

select * from table3  t3 
join table1 t1 on t1.id = t3.table2_id     
join table2 t2 on t2.id = t3.table1_id    
Where t3.table2_id <> 0 or  t3.table1_id    <> 0    

使用直接连接Where

Answer 2

(select * from table3 as t3 join table1 as t1 on t1.id = t3.id and t3.table1_id != 0)
UNION
(select * from table3 as t3 join table2 as t2 on t2.id = t3.id and t3.table2_id != 0)