Question

需要一些子查询帮助

如果我有这样的1个查询：

SELECT Learner.Learner_Id, Max(LearnerEmploymentStatus.DateEmpStatApp) AS LatestEmpDate, Learner.LearnRefNumber, Learner.FamilyName, Learner.GivenNames, EmploymentStatusMonitoring.ESMType
FROM (Learner LEFT JOIN LearnerEmploymentStatus ON LearnerEmploymentStatus.Learner_Id = LearnerEmploymentStatus.Learner_Id) LEFT JOIN EmploymentStatusMonitoring ON LearnerEmploymentStatus.LearnerEmploymentStatus_Id = EmploymentStatusMonitoring.LearnerEmploymentStatus_Id
WHERE EmploymentStatusMonitoring.ESMType="BSI"
GROUP BY Learner.Learner_Id, Learner.LearnRefNumber, Learner.FamilyName, Learner.GivenNames, EmploymentStatusMonitoring.ESMType

......和另一个这样：

SELECT Learner.Learner_Id, LearnerEmploymentStatus.DateEmpStatApp, EmploymentStatusMonitoring.ESMCode
FROM (Learner LEFT JOIN LearnerEmploymentStatus ON Learner.Learner_Id = LearnerEmploymentStatus.Learner_Id) LEFT JOIN EmploymentStatusMonitoring ON LearnerEmploymentStatus.LearnerEmploymentStatus_Id = EmploymentStatusMonitoring.LearnerEmploymentStatus_Id

...我想在两个查询之间进行联接（对常见的Learner_Id和LatestEmpDate / DateEmpStatApp字段进行LEFT JOIN），我将如何进行所有操作这个工作在一个查询中，上面的2个查询将是子查询？

我的下面尝试未被接受（不支持JOIN表达式）：

SELECT sQ1.Learner_Id, sQ1.LearnRefNumber, sQ1.FamilyName, sQ1.GivenNames, sQ1.LatestEmpDate, sQ1.ESMType, sQ2.ESMCode
FROM
(SELECT Learner.Learner_Id, Max(LearnerEmploymentStatus.DateEmpStatApp) AS LatestEmpDate, Learner.LearnRefNumber, Learner.FamilyName, Learner.GivenNames, EmploymentStatusMonitoring.ESMType
FROM (Learner LEFT JOIN LearnerEmploymentStatus ON LearnerEmploymentStatus.Learner_Id = LearnerEmploymentStatus.Learner_Id) LEFT JOIN EmploymentStatusMonitoring ON LearnerEmploymentStatus.LearnerEmploymentStatus_Id = EmploymentStatusMonitoring.LearnerEmploymentStatus_Id
WHERE EmploymentStatusMonitoring.ESMType="BSI"
GROUP BY Learner.Learner_Id, Learner.LearnRefNumber, Learner.FamilyName, Learner.GivenNames, EmploymentStatusMonitoring.ESMType) As sQ1
LEFT JOIN
(SELECT Learner.Learner_Id, LearnerEmploymentStatus.DateEmpStatApp, EmploymentStatusMonitoring.ESMCode
FROM (Learner LEFT JOIN LearnerEmploymentStatus ON Learner.Learner_Id = LearnerEmploymentStatus.Learner_Id) LEFT JOIN EmploymentStatusMonitoring ON LearnerEmploymentStatus.LearnerEmploymentStatus_Id = EmploymentStatusMonitoring.LearnerEmploymentStatus_Id) As sQ2
ON (sQ1.Learner_Id = sQ2.Learner_Id) AND (sQ1.LatestEmpDate = sQ2.DateEmpStatApp);

Answer 1

这样的事情会让你得到你想要的......？

SELECT l.Learner_Id, d.LatestEmpDate, l.LearnRefNumber, l.FamilyName, l.GivenNames, m.ESMType, m.ESMCode
FROM ((Learner AS l
  LEFT JOIN (
    SELECT s.Learner_Id, MAX(s.DateEmpStatApp) AS LatestEmpDate
    FROM LearnerEmploymentStatus AS s
    GROUP BY s.Learner_Id) AS d ON d.Learner_Id = l.Learner_Id)
  LEFT JOIN LearnerEmploymentStatus AS ls ON (ls.Learner_Id = d.Learner_Id) AND (ls.DateEmpStatApp = d.LatestEmpDate))
  LEFT JOIN EmploymentStatusMonitoring AS m ON m.LearnerEmploymentStatus_Id = ls.LearnerEmploymentStatus_Id
WHERE m.ESMType = 'BSI'

假设同一个学习者不会两次获得相同的DateEmpStatApp，这可能有效或无效。

MS-Access加入2个子查询

1 个答案: