如何有效使用SQL连接

Question

表

工作

JobId, JobName  

的JobDetail

JobDetailId, JobId, AcctNum, PerformDate

一个Job包含由JobId链接的许多JobDetails 。

对于某些JobNames ，（JobeName1，JobName2），我想要一个仅包含一个JobDetail的列表，其中Performdate在过去6个月内。

对于上述标准，我应该获得两个记录。 什么是正确的SQL语句？

我已经做到了这一点，而不仅仅是获得正确的陈述。

SELECT 
    COUNT(J.JobId) 
FROM 
    Job J  
WHERE 
    J.JobName IN ('Doc1', 'Doc2')
GROUP BY 
    J.JobName

[编辑]
SQL Server 2005

[EDIT2]

SELECT 
    J.JobName, JD.AcctNum 
FROM 
    Job J  
JOIN JobDetail JD ON J.JobId = JD.JobId
WHERE 
    J.JobName IN ('DOC1', 'DOC2')
GROUP BY 
    J.JobName

该语句产生：

J.JobId在选择列表中无效...未包含在聚合函数中。

[EDIT3]
http://sqlfiddle.com/#!3/3ef21/1/0

我想要由PerformDate为Doc1和DOC2提供的最新AcctNum。

因此，从SQLFIDDLE中的数据中，我应该为每个JobName返回2个ROWS。

[EDIT4]
我的预期数据是JobDetail表中的*行：
JobDetailId 1
jobDetailId 3

Answer 1

干得好：

SELECT COUNT(J.JobId) FROM Job J  
INNER JOIN JobDetails D ON J.JobId = D.JobId
WHERE J.JobName IN ('Jobname1', 'Jobname2') 
AND D.PerformDate >= DateAdd(mm, -6, getdate())
GROUP BY J.JobName

我已经在TSQL（SQL Server）中编写了此代码。 对于其他DBMS，您将必须对DateAdd(mm, -6, getdate())使用相关的函数。

更新：要选择最新AcctNum的DOC1和DOC2 。

 
 
  
  
 
  Select D.JobID, Acctnum from 
    JobDetail D Inner Join
    (
     SELECT J.JOBID, MAX(PerformDate) as LatestPerformDate FROM Job J
     INNER JOIN JobDetail D ON J.JobId = D.JobId
     WHERE J.JobName IN ('DOC1', 'DOC2') 
     Group by J.JobID
    ) X on D.JobID = X.JobID
    And D.PerformDate = X.LatestPerformDate
 

 
 

更新2：当DOC2可以在Job表中以不同的JobID出现两次时。

Select D.JobID, Acctnum from 
JobDetail D Inner Join Job J on J.JobID = D.JobID
Inner join
(
 SELECT J.JOBname, MAX(PerformDate) as LatestPerformDate FROM Job J  
 INNER JOIN JobDetail D ON J.JobId = D.JobId
 WHERE J.JobName IN ('DOC1', 'DOC2')
 group by j.jobname
) X on J.JobName = X.JobName
And D.PerformDate = X.LatestPerformDate

问题中sqlfiddle中发布的输入数据的输出：

JOBID   ACCTNUM
--------------------
 1      1235
 4      1238

Answer 2

SELECT j.*, d.*
FROM Job j
JOIN (SELECT JobId, MAX(PerformDate) maxDate
      FROM JobDetail
      WHERE PerformDate > DATEADD(mm, -6, GETDATE())
      GROUP BY JobId) md
ON j.JobId = md.JobId
JOIN JobDetail d
ON d.JobId = md.JobId AND d.PerformDate = md.maxDate
WHERE j.JobName IN ('DOC1', 'DOC2');

小提琴