MySql查询连接返回结果与空列

Question

你好我有这个查询我希望它也返回表j行（jobcard）其中j.articleId，j.statusId，j.hcwsId，j.gpId为null任何帮助PLZ ？

SELECT jobcardId,createDateTime,jobNo,companyId, 
         customerId,serialNo,rsvdDate,model,promiseDate, 
         readyDate,deliveryDate,cashMemoNo,dealer, 
         dop,status,warrantyCardno,batchNo, 
         employeeId,hcws,gp,cdId, 
         collectionDate,remarks,article 
       FROM jobcard j, articles a, statuses s, hcws h, gp g 
       WHERE j.articleId=a.articleId AND 
         j.statusId = s.statusId AND 
         j.hcwsId = h.hcwsId AND 
         j.gpId=g.gpId" 

Answer 1

你不是因为你的内部连接均不含它们的那些列越来越NULL值 - 他们不与其他表中的任何匹配。

要包含空值，使用OUTER JOIN：

SELECT jobcardId,createDateTime,jobNo,companyId, 
    customerId,serialNo,rsvdDate,model,promiseDate, 
    readyDate,deliveryDate,cashMemoNo,dealer, 
    dop,status,warrantyCardno,batchNo, 
    employeeId,hcws,gp,cdId, 
    collectionDate,remarks,article 
FROM jobcard j 
LEFT OUTER JOIN articles a ON j.articleId=a.articleId 
LEFT OUTER JOIN statuses s ON j.statusId = s.statusId 
LEFT OUTER JOIN hcws h ON j.hcwsId = h.hcwsId 
LEFT OUTER JOIN gp g ON j.gpId=g.gpId 

Answer 2

使用LEFT JOIN。您现在的查询有效地工作为INNER JOIN，排除没有匹配的行。使用LEFT JOIN，您将返回jobcard中的所有行，并在其中包含没有匹配记录的其他表中的列（如，jobcard包含该列的NULL）时返回NULL。

SELECT jobcardId,createDateTime,jobNo,companyId, 
         customerId,serialNo,rsvdDate,model,promiseDate, 
         readyDate,deliveryDate,cashMemoNo,dealer, 
         dop,status,warrantyCardno,batchNo, 
         employeeId,hcws,gp,cdId, 
         collectionDate,remarks,article 
FROM 
    jobcard j 
    LEFT JOIN articles a on j.articleId=a.articleId 
    LEFT JOIN statuses s on j.statusId = s.statusId 
    LEFT JOIN hcws h j.hcwsId = h.hcwsId 
    LEFT JOIN gp g on j.gpId=g.gpId