Get distinct values from a datatable or String? - sql

Question

I have created the Datatable below which feeds a GridView on Page_Load
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
At present it outputs values:
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
I would like to get my DataTable below to output distinct rows like this:
SetName t_date o_id
name1 12.12.12 1
name2 13.07.12 1
name3 16.07.12 4
can anybody tell me hw this can be achieved?

Answer 1

It looks like you want the earliest date for each name. If so, you could use a Group By and the min function:
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