左外连接子查询？

Question

----------
User
----------
user_ID(pk)
UserEmail

----------
Project_Account
----------
actno
actname
projno
projname
ProjEmpID
ProjEmpMGRID

其中ProjEmpID,ProjEmpMGRID是user_id,ProjEmpMGRID可以为null.我需要查找useremail并显示表project_account.我需要使用具有重复值的actNo进行查询.

我的查询是这样的:

 select projno,projname,actno,actname,
(select u.user_email as project_manager from project_account c left outer join users u
     on u.user_id = c.ProjEmpID where actno='some no')as project_manager,

     (select u.user_email as program_manager from project_account c left outer join users u
        on u.user_id = c.ProjEmpMGRID where actno='someno') as program_manager

        from project_account where actno='someno'

我在Oracle中收到的错误消息:

ora-01427单行子查询返回多行

当我的子查询返回多个电子邮件ID时,我收到此错误.正如我所说,行为不是不唯一的.我能理解错误,但我无法弄清楚解决方案.我在子查询中执行左外连接,因为prog manager id中可能有空值.

任何帮助,将不胜感激.

Answer 1

您得到的错误是您的一个子查询(对于project_manager或program_manager)根据您的条件为您提供了多个ID.这是有道理的,因为多个项目帐户可能具有相同的"actno",因为您没有将其指定为Primarky Key(pk)

而不是使用子查询,只需直接连接到用户表以查找ID

 select projno,projname,actno,actname,
  project_user.user_email as project_manager,
  program_user.user_email as program_manager
    from project_account 
    left join User as project_user
      on project_account.ProjEmpID = project_user.user_id
    left join User as program_user
      on project_account.ProjEmpMGRID = program_user.user_id

where actno='someno'