SQL 选择与二进制搜索

Question

只是为了记录我要添加的未来问题 将数据提取到datagridview，我知道代码远非水晶般清晰，只是为了理解这个主题的属性。

    CreateDataTable(Me.t, "SELECT * FROM tblContacts", "tblContacts")
    CreateDataTable(Me.t2, "SELECT * FROM ContactsData", "ContactsData")

    Dim joined = From row1 In t.AsEnumerable()
                   Join row2 In t2.AsEnumerable()
                   On row1.Field(Of Int32)("ID") Equals row2.Field(Of Int32)("ID")
                   Select BothRows = New With {row1, row2}






    With DataGridView1
        .Columns.Clear()
        .Rows.Clear()
        ' add columns of tblContacts table
        For i = 0 To joined.AsEnumerable.First.row1.Table.Columns.Count - 1
            .Columns.Add(joined.AsEnumerable.First.row1.Table.Columns(i).ColumnName.ToString, joined.AsEnumerable.First.row1.Table.Columns(i).ColumnName.ToString)
        Next
        ' add columns of ContactsData table
        For i = 0 To joined.AsEnumerable.First.row2.Table.Columns.Count - 1
            .Columns.Add(joined.AsEnumerable.First.row2.Table.Columns(i).ColumnName.ToString, joined.AsEnumerable.First.row2.Table.Columns(i).ColumnName.ToString)
        Next
        ' add rows to datagridview
        .Rows.Add((joined.Count - 1))

    End With

    Dim rownum As Integer = 0
    For Each x In joined

        Dim row1 As DataRow = x.row1
        Dim row2 As DataRow = x.row2

        ' populate data to dgv
        For i = 0 To row1.Table.Columns.Count - 1
            DataGridView1.Rows(rownum).Cells(i).Value = row1.Item(i).ToString
        Next

        For i = row1.Table.Columns.Count To DataGridView1.Columns.Count - 1
            DataGridView1.Rows(rownum).Cells(i).Value = row2.Item(i - row1.Table.Columns.Count).ToString
        Next

        rownum += 1
    Next

---

经过测试@Tim 的回答如下： 我对 linq to dataset 进行了测试，但出现错误，我不知道为什么.. 错误描述是'值不能为空。参数名称：source' 以防万一我测试了一个常规的 SQL 内连接查询并且它工作正常。

我在 access 中创建了 2 个表，这是这些表

 tblCOntacts
 --------------
 ID FirstName   LastName
 ---------------------------------
 22 John        Smith
 23 Jane        Apple
 24 Jonathan    Tucker


 ContactsData
 --------------
 ID Proffesion  Hoby
 ---------------------------------
 22 Carpenter   Long Runs
 23 Pilot       Gym
 24 Psychologyst    Programming

这是我的代码，我注释了导致错误的行：

 Private Sub Button4_Click(sender As System.Object, e As System.EventArgs)           Handles Button4.Click
     CreateDataTable(Me.t, "SELECT * FROM tblContacts", "tblContacts")
    CreateDataTable(Me.t2, "SELECT * FROM ContactsData", "ContactsData")

   Dim joined = From row1 In t.AsEnumerable()
                  Join row2 In t2.AsEnumerable()
                  On row1.Field(Of Int32)("ID") Equals row2.Field(Of Int32)("ID") ' here i get the error: Value cannot be null. Parameter name: source
                  Select BothRows = New With {row1, row2}

    For Each x In joined
        Dim row1 As DataRow = x.row1
        Dim row2 As DataRow = x.row2
    Next
 end sub


   Public con As OleDbConnection
   Public dset As DataSet
   Public ad As OleDbDataAdapter
   Public cmd As OleDbCommand
   Public t As DataTable
Public t2 As DataTable

  Private Sub CreateDataTable(ByVal tb As DataTable, ByVal query As String,   ByVal table As String)
         Dim q As String = query
    con = New OleDbConnection
    con.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\Users\Jonathan\Desktop\בסיס נתונים access\AddressBook.mdb"

    con.Open()
    dset = New DataSet
    cmd = New OleDbCommand(query, con)
    ad = New OleDbDataAdapter(cmd)
    ad.Fill(dset, table)
    con.Close()

    ' query dataset with linq
    tb = dset.Tables(table)
 end sub

---

我有 2 个来自不同 Access 数据库的数据表（所以我不能使用 SQL 连接语句），我需要通过相同的数字主键匹配来自 2 个表的记录中的 2 列。 我正在考虑 2 个选项：

1. 多个 SQL SELECT 查询。
2. 使用 Visual Basic 对 2 个数据表对象进行二分搜索。

什么方法更有效？更专业？这样做的正确方法是什么？

坦克

Answer 1

就效率和更重要的可读性和可维护性而言，最好的方法是使用Linq-To-DataSet：

Dim joined = From row1 In table1.AsEnumerable()
             Join row2 In table2.AsEnumerable()
             On row1.Field(Of Int32)("ID") Equals row2.Field(Of Int32)("ID")
             Select BothRows = New With {row1, row2}

For Each x In joined
    Dim row1 As DataRow = x.row1
    Dim row2 As DataRow = x.row2
Next

您需要添加Imports System.Linq。 Enumerable.Join 是高效的，因为它使用了一个集合。