vb.net 中的内连接 SQL 语法

Question

这是我用来显示类别选择的select SQL语法，但我需要做的是显示根据设备ID选择的相应类别

我有 2 个表，tblOfficeEquipmentCategory 和 tblOfficeEquipmentProfile

我需要内部加入 tblOfficeEquipmentProfile 以便我可以添加 WHERE equipment_id = '"txtid.text"'

相应的 SQL 语法是什么

Public Sub DisplayCategory()
    'based on oe_id
    Dim sqlconn As New SqlClient.SqlConnection
    sqlconn.ConnectionString = "server = SKPI-APPS1;" & _
    "Database = EOEMS;integrated security=true"

    Dim sqlcommand As SqlCommand

    sqlconn.Open()
    Dim da As New SqlDataAdapter("select * from tblOfficeEquipmentCategory", sqlconn)
    Dim dt As New DataTable
    da.Fill(dt)
    cmbCategory.DataSource = dt
    cmbCategory.ValueMember = "CAT_Name"
    cmbCategory.DisplayMember = "CAT_ID"
    sqlconn.Close()
End Sub

Answer 1

假设equipment_id位于表tblOfficeEquipmentProfile和列CAT_ID上，该列CAT_ID其链接到表tblOfficeEquipmentCategory 。

SELECT  a.CAT_Name
FROM    tblOfficeEquipmentCategory a
        INNER JOIN tblOfficeEquipmentProfile b
            ON a.CAT_ID = b.CAT_ID
WHERE   b.equipment_id = @ID

要进一步了解有关联接的更多信息，请访问以下链接：

• SQL 连接的可视化表示

Answer 2

最好开始考虑如何将数据访问与演示代码分开。 你需要这样的东西：

Public Function DisplayCategory() 
    cmbCategory.ValueMember = "CAT_Name"
    cmbCategory.DisplayMember = "CAT_ID"
    cmbCategory.DataSource = GetEquipmentCategories(Convert.ToInt32(txtid.text))
End Sub

Public Function GetEquipmentCategories(ByVal EquipmentID As Integer) As DataTable
    'based on oe_id

    Dim sql As String = "SELECT a.CAT_ID, a.CAT_Name" & _ 
                       " FROM tblOfficeEquipmentCategory a" & _
                       " INNER JOIN tblOfficeEquipmentProfile b ON a.CAT_ID = b.CAT_ID" & _
                       " WHERE b.equipment_id = @ID"

    Dim result As New DataTable
    Using cn New SqlConnection("server=SKPI-APPS1;Database=EOEMS;integrated security=true"), _
          cmd As new SqlCommand(sql, cn)

        cmd.Parameters.Add("@ID", SqlDbType.Int).Value = EquipmentID

        cn.Open()
        Using rdr As SqlDataReader = cmd.ExecuteReader
            result.Load(rdr)
        End Using
    End Using
    Return result
End Function

Answer 3

        Dim sql = "Select  Authors.Au_ID, Authors.Author, [Title Author].ISBN FROM(Authors INNER JOIN [Title Author] ON Authors.Au_ID = [Title Author].Au_ID)"

Answer 4

   Try
        con.Open()
        Dim cmd As New OleDb.OleDbCommand
        Dim dt As New DataTable
        Dim da As New OleDb.OleDbDataAdapter
        Dim sql = "Select  Authors.Au_ID, Authors.Author, [Title Author].ISBN FROM(Authors INNER JOIN [Title Author] ON Authors.Au_ID = [Title Author].Au_ID)"
        cmd.Connection = con
        cmd.CommandText = sql
        da.SelectCommand = cmd
        da.Fill(dt)
        DGV2.DataSource = dt
        con.Close()
    Catch ex As Exception
        MsgBox(ex.Message)
    End Try