从sql查询中获取空结果
我有一个疑问:从sql查询中获取空结果,sql,select,join,Sql,Select,Join,我有一个疑问: select p1.cost as V1, p2.cost as V2 , p3.cost as V3 from product p1, product p2, product p3 where p1.id =1 and p2.id =2 and p3.id=3 在我的产品表中,我只有一行: id | name | cost 1 | product1 | 20 正如您在这里看到的,我将得到空结果! 但我如何才能得到: V1 | V2 | V
select p1.cost as V1, p2.cost as V2 , p3.cost as V3
from product p1, product p2, product p3
where p1.id =1 and p2.id =2 and p3.id=3
在我的产品表中,我只有一行:
id | name | cost
1 | product1 | 20
正如您在这里看到的,我将得到空结果!
但我如何才能得到:
V1 | V2 | V3
20 | |
可以使用左连接:
SELECT p1.cost AS V1, p2.cost AS V2 , p3.cost AS V3
FROM product p1
LEFT JOIN product p2 on p2.id = 2
LEFT JOIN product p3 on p3.id = 3
WHERE p1.id = 1
可能是
其中p1.id=1
?