sql - 从数据表或字符串中获取不同的值？

Question

我在下面创建了 Datatable，它在 Page_Load 上提供了一个 GridView

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

    Dim strQuery As String = "SELECT DISTINCT setsTbl.setName, trainingTbl.t_date, userAssessmentTbl.o_id FROM userAssessmentTbl LEFT JOIN trainingTbl ON userAssessmentTbl.tt_id = trainingTbl.tt_id LEFT JOIN setsTbl ON trainingTbl.s_id = setsTbl.s_id LEFT JOIN outcomesTbl ON userAssessmentTbl.o_id = outcomesTbl.o_id WHERE UserId = @UserId ORDER BY setName, t_date DESC "

    Dim cmd As New SqlCommand(strQuery)
    cmd.Parameters.AddWithValue("@UserId", userString)
    Dim dt As DataTable = GetData(cmd)

   GridView1.DataSource = dt
   GridView1.DataBind()

End Sub

目前它输出值：

SetName t_date o_id
name1 12.12.12 1
name2 13.07.12 1
name2 15.07.12 2
name3 16.07.12 4
name3 17.07.12 3

我想让我的 DataTable 下面输出不同的行，如下所示：

SetName t_date o_id
name1 12.12.12 1
name2 13.07.12 1
name3 16.07.12 4

谁能告诉我这是怎么做到的？

Answer 1

看起来您想要每个名称的最早日期。如果是这样，您可以使用 Group By 和 min 函数：

setsTbl.setName, Min(trainingTbl.t_date), Min(outcomesTbl.o_id)
FROM userAssessmentTbl LEFT JOIN trainingTbl ON userAssessmentTbl.tt_id = trainingTbl.tt_id 
LEFT JOIN setsTbl ON trainingTbl.s_id = setsTbl.s_id LEFT JOIN outcomesTbl 
ON userAssessmentTbl.o_id = outcomesTbl.o_id 
WHERE UserId = @UserId Group By setsTbl.setName ORDER BY setsTbl.setName