Sql server 2008 合并两个表中的数据，其中一个表优先

我试图将两个表中的数据合并到一个结果中，但不复制

CourseID

中的id，结果中优先考虑用户的补全

用户课程完成表 课程分组表 预期结果 我想找到一个用户的所有课程完成情况，并用未完成的项目补充该列表。例如，如果我想要组

1

和用户

1

的列表，我会得到

CourseID, SystemComplete, UserComplete
======================================
1, NULL, 12/06/2012
2, NULL, 12/06/2012
3, 10/06/2012, 12/06/2012
4, NULL, NULL
12, NULL, NULL --not in completion record

我试过的 我试过几个问题，但我似乎无法解决这个问题。下面的那个是我在里面找到的东西

…但这只返回一行结果

我得到的最接近的结果是

UNION

ing两个查询，但是我不知道如何将

UserComplete

和

SystemComplete

数据放入查询中

SELECT CourseID
FROM UserCompletion
WHERE
  EmployeeID = 1

UNION

SELECT CourseID
FROM CoursesToGroup
WHERE
  LearningPathID = 1

这将为

CourseID

返回正确的结果，但是，正如我前面所述，我不知道如何将完成数据放在那里，并且仍然删除重复的

CourseID

我错过了什么

SELECT CourseID, SystemComplete, UserComplete
FROM UserCompletion
WHERE
UserId = 1

UNION

SELECT CourseId, null, null
FROM CoursesToGroup
where GroupId = 1
and CourseId NOT IN 
    (SELECT CourseId From UserCompletion
     WHERE UserId = 1)

SELECT
  COALESCE(uc.CourseID, cg.CourseID) as CourseID
FROM
  CoursesToGroup as cg
FULL JOIN UserCompletion as uc ON
  uc.CourseID = cg.CourseId
WHERE
  uc.UserID = 1 AND
  cg.GroupID = 1

SELECT CourseID
FROM UserCompletion
WHERE
  EmployeeID = 1

UNION

SELECT CourseID
FROM CoursesToGroup
WHERE
  LearningPathID = 1

SELECT CourseID, SystemComplete, UserComplete
FROM UserCompletion
WHERE
UserId = 1

UNION

SELECT CourseId, null, null
FROM CoursesToGroup
where GroupId = 1
and CourseId NOT IN 
    (SELECT CourseId From UserCompletion
     WHERE UserId = 1)