Question

我加入2桌有问题这是mysql查询

选择* 来自tbl_perspective a 内部联接tbl_objective b on b.idperspective = a.idperspective

我想显示第一行的perspectivename和空白或null

Answer 1

加入一个子查询，该子查询标识每个idperspective组的第一行：

SELECT t1.*
FROM tbl_perspective t1
INNER JOIN
(
    SELECT idperspective, MIN(idobjective) AS min_idobjective
    FROM tbl_perspective
    GROUP BY idperspective
) t2
    ON t1.idperspective = t2.idperspective AND
       t1.idobjective   = t2.min_idobjective;

Answer 2

您需要使用LEFT JOIN来包含所有结果，例如：https://www.codeproject.com/Articles/33052/Visual-Representation-of-SQL-Joins

Answer 3

嗨Anwr Rawk只需你可以使用LEFT JOIN

 select * from tbl_perspective as a 
     left join 
 tbl_objective as b 
 on b.idperspective=a.idperspective

Answer 4

感谢您的回答，2表加入时确定没关系，但加入3表时我有问题。这是我的查询

    select 
case when b.idobjective=(select min(idobjective) from tbl_objective where idperspective=c.idperspective) then c.perspectivename end as perspectivename,
case when a.idindicator=(select min(idindicator) from tbl_indicator where idobjective=a.idobjective) then b.objectivename end as objectivename,
a.indicatorname
from tbl_indicator a
inner join tbl_objective b on b.idobjective=a.idobjective
inner join tbl_perspective c on c.idperspective=b.idperspective

此图片是结果查询，但我希望仅在财务时显示财务，并且所有行都显示为null this result

Mysql查询连接表，如果值相同则填充空

4 个答案: