SQL Server案例语句

我试图编写一个查询，每个

employeerid

只生成一行，而不是每个雇主生成多行，一次只填充一列。我的查询结果如下：

我使用的查询是：

SELECT Employer.employerid,
    CASE WHEN Service.xxserviceid = '1' THEN 'Number 1' ELSE 'NULL' END AS Service1,
    CASE WHEN Service.xxserviceid  = '2' THEN 'Number 2' ELSE 'NULL' END AS Service2,
    CASE WHEN Service.xxserviceid  = '3' THEN 'Number 2' ELSE 'NULL' END AS Service3
FROM Employer
INNER JOIN Service
ON Service.employerid = Employer.employerid;

---

因此，我希望每个雇主在一行中填写

Service1

，

Service2

，

Service3

，而不是在多行中填写

您可以使用

分组依据

+

MAX

将结果减少到每个员工一行：

SELECT Employer.employerid,
  max(CASE WHEN Service.xxserviceid = '1' THEN 'Number 1' ELSE 'NULL' END) AS Service1,
  max(CASE WHEN Service.xxserviceid  = '2' THEN 'Number 2' ELSE 'NULL' END) AS Service2,
  max(CASE WHEN Service.xxserviceid  = '3' THEN 'Number 3' ELSE 'NULL' END) AS Service3
FROM Employer
INNER JOIN Service
  ON Service.employerid = Employer.employerid
GROUP BY Employer.employerid;

但是，如果您仔细考虑一下，您甚至不需要与

Employer

表连接，因为您从中使用的只是

employerid

列，该列已经存在于

服务中

因此，查询可以简化为：

SELECT employerid,
  max(CASE WHEN xxserviceid = '1' THEN 'Number 1' ELSE 'NULL' END) AS Service1,
  max(CASE WHEN xxserviceid  = '2' THEN 'Number 2' ELSE 'NULL' END) AS Service2,
  max(CASE WHEN xxserviceid  = '3' THEN 'Number 3' ELSE 'NULL' END) AS Service3
FROM Service
GROUP BY employerid;

SQLFiddle:
据我所知，您可能只需要一个服务专栏。
这篇文章中提供的其他答案应该有用。但是，如果您只需要一个服务列，可以尝试以下操作：

SELECT Employer.employerid,
    'Number ' + Max(Service.xxserviceid) AS Service1
FROM Employer
INNER JOIN Service
ON Service.employerid = Employer.employerid;
GROUP BY Employer.employerid

SELECT Employer.employerid,
    'Number ' + Max(Service.xxserviceid) AS Service1
FROM Employer
INNER JOIN Service
ON Service.employerid = Employer.employerid;
GROUP BY Employer.employerid