SQL内部将多个表连接到类似键上的一个表

Question

我正在开发一个项目，其中包含一个Employee表，其中包含EmployeeID（Int）键入的所有员工的所有名称

我还有一个Job表，其中包括JobName as string和Foreman，ProjectManager，Project Coordinator，AccountManager as INT，它们链接回Employee表。

我需要能够从员工表中提取分配给该工作的每个员工的名字和姓氏。我已经尝试过下面的查询，但没有产生任何结果。

我错过了什么......

SELECT
    j.jobsitename,
    j.jobsiteaddress, 
    CONCAT( RTRIM( e.empFirstName ), ' ', RTRIM( e.empLastName ) ) AS Foreman,
    CONCAT( RTRIM( pm.empFirstName ), ' ', RTRIM( pm.empLastName ) ) AS ProjectManager,
    CONCAT( RTRIM( pc.empFirstName ), ' ', RTRIM( pc.empLastName ) ) AS  ProjectCoordinator
FROM
    mpjob AS j 
    INNER JOIN mpEmployee AS e  ON j.jobforeman   = e.empemployeeid
    INNER JOIN mpEmployee AS pm ON j.jobProjMgr   = pm.empemployeeid
    INNER JOIN mpEmployee AS pc ON j.jobProjCoord = pc.empemployeeid

Answer 1

SELECT
   j.jobsitename,
   j.jobsiteaddress,
   e.empFirstName as ForemanFirstName,
   e.empLastName as ForemanLastName,
   pm.empFirstName as PmFirstName,
   pm.empLastName as PmLastName,
   pc.empFirstName as PcFirstName,
   pc.empLastName as PcLastName
FROM mpjob AS j
LEFT JOIN mpEmployee AS e ON j.jobforeman = e.empemployeeid
LEFT JOIN mpEmployee AS pm ON j.jobProjMgr = pm.empemployeeid
LEFT JOIN mpEmployee AS pc ON j.jobProjCoord = pc.empemployeeid

LEFT JOIN这些值。 如果有工头，PM和PC，INNER JOIN将返回这些值。 LEFT JOIN显示mpJob中的所有数据，即使没有。