Question

我有两个如下表

Table A
ID   ID_Name    Amount
------------------------
1    ABC        200
2    XYZ        300

Table B
ID    Role    Name 
------------------
1     Plumber   John
1     Estimator  Redmond

我想同时连接两个表，并且需要以下结果


ID ID_Name  Plumber Estimator   Amount
--------------------------------------
1   ABC     John      Redmond   200

我正在使用的SQL加入

Select A.ID, A.ID_Name

CASE WHEN B.Role='Plumber' THEN B.Name END AS Plumber,
CASE WHEN B.Role='Estimator' THEN B.Name END AS Estimator,
A.Amount
FROM A A
INNER JOIN B B ON A.ID=B.ID

```
How I can achieve this, when am trying to join I am getting two lines for the same ID and if do group by amount is 400

Answer 1

您应该两次加入tableb，一次是Plumber，另一次是estimator

select a.ID,  a.ID_Name, b1.name plumber, b2.name estimator, a.amount
from tableA a
inner join tableb b1 on a.id = b1.id and b1.role ='Plumber'
inner join tableb b2 on a.id = b2.id and b2.role ='Estimator'

如果有重复的行，则应使用不同的

select distinct  a.ID,  a.ID_Name, b1.name plumber, b2.name estimator, a.amount
from tableA a
inner join tableb b1 on a.id = b1.id and b1.role ='Plumber'
inner join tableb b2 on a.id = b2.id and b2.role ='Estimator'

Answer 2

虽然@scaisEdge可以在给定的情况下工作，但我想您必须重新考虑表B的架构。期望的结果是动态的。现在，使用上面给出的查询，您将排成一行。如果引入另一个新角色会发生什么？

如果Plumber和Estimator是给定ID的强制实体，而不仅仅是TableB.Role可能像TableB.Plumber，TableB.Estimator一样重新设计。

避免在SQL JOIN上重复

2 个答案: