Question

我有一个包含三个表的数据库。 “名册”，“培训课程”和“课程注册” 名册和课程注册通过“ETID”（员工培训ID）连接。课程注册和培训课程通过“课程ID”连接我正在尝试创建一个将返回所有员工的查询，并为所有课程创建一个YES / NO值。我写了以下内容来了解具体的员工，但我似乎无法找到返回所有员工的正确方法。任何帮助将不胜感激。

SELECT [TRAINING COURSES].[course id]
     , [TRAINING COURSES].[course name]
     , "YES" AS Completed
     , [COURSE ENROLLMENT].[training date]
FROM [TRAINING COURSES] 
INNER JOIN [COURSE ENROLLMENT]
            ON [COURSE ENROLLMENT].[course id]=[TRAINING COURSES].[course id]
WHERE [COURSE ENROLLMENT].[ETID]=[ENTER ETID]

UNION ALL 

SELECT [TRAINING COURSES].[course id]
     , [TRAINING COURSES].[course name]
     , "No" AS Completed
     , NULL
FROM [TRAINING COURSES]
WHERE NOT EXISTS 
(
    SELECT *
    FROM [COURSE ENROLLMENT]
    WHERE [COURSE ENROLLMENT].[course id]=[TRAINING COURSES].[course id] 
    AND [COURSE ENROLLMENT].[ETID]=[ENTER ETID:]
)
ORDER BY [TRAINING COURSES].[course name];

Answer 1

您不需要在此查询中使用Union。使用LEFT OUTER JOIN替换INNER JOIN，它将完成与查询相同的操作，但性能会更好。

SELECT [Training Courses].[Course Id], [Training Courses].[Course Name], 
        IIF(IsNull([Course Enrollment].[ETID]), "NO", "YES") as Completed,
        [Course Enrollment].[Training Date]
FROM    [Training Courses]
        LEFT OUTER JOIN [Course Enrollment]
            ON [Training Courses].[Course Id] = [Course Enrollment].[Course Id] 
ORDER BY [Training Courses].[Course Name]

如果您想要所有员工和所有课程，您需要在名册和培训课程表之间进行交叉连接。然后，您将使用课程注册表进行左连接，以获得上面的“是”。

Answer 2

从两个子查询中删除WHERE [COURSE ENROLLMENT].[ETID]=[ENTER ETID]。

试图创建一个将返回所有记录的查询让我感到难过

2 个答案: