Question

我很难弄清楚如何进行左连接并拉出连接为空的记录，或者连接工作，但是支付的列是0.这是sql I＆＃39; m试图重新创建

SELECT * 
    FROM JobsCompleted
    LEFT JOIN SqWar ON JobsCompleted.JobFk = SqWar.JobFk
    WHERE SqWar.SqWarId IS NULL OR SqWar.Paid = 0

这是我迄今为止在linq中所拥有的。

'not sure here how I do if the join is null, or joins, but paid is 0
            Dim jobIds = (From jc In db.JobsCompleteds
                          Group Join sqw In db.SqWars On sqw.JobFk Equals jc.JobFk Into SqGroup = Group
                          Where jc.DateCompleted >= fromInput.SelectedDate And jc.DateCompleted <= toInput.SelectedDate And
                              SqGroup Is Nothing) 'not sure here how I do if it's null or paid = 0

Answer 1

使用Group Join，如果你想要一个SQL LEFT JOIN，特别是因为你想要从右侧测试一个字段，你需要使用第二个From子句DefaultIfEmpty：

Dim jobIds = From jc In db.JobsCompleteds
             Group Join sqw In db.SqWars On sqw.JobFk Equals jc.JobFk Into Group
             From sqw In Group.DefaultIfEmpty()
             Where sqw Is Nothing Or sqw.Paid = 0
             Select New With { jc, sqw }

请注意，LINQ没有直接等效于SQL SELECT *所以我返回了一个带有子对象的匿名对象。如果您希望将结果展平，则必须明确列出所有字段。

如果您想处理加入组，您还可以按标准过滤每个组：

Dim jobIdsG = From jc In db.JobsCompleteds
              Group Join sqw In db.SqWars On sqw.JobFk Equals jc.JobFk Into Group
              Select New With {jc, .sqGroup = Group.Where(Function(sq) sq.Paid = 0)}

VB.net linq左连接为null或0

1 个答案: