替代T-SQL AS关键字

Question

Please see the code below:

Imports System.Data.SqlClient
Imports System.Configuration

    Public Class Form1
        Private _ConString As String
        Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
            Dim objDR As SqlDataReader
            Dim objCommand As SqlCommand
            Dim objCon As SqlConnection
            Dim id As Integer
            Try
                _ConString = ConfigurationManager.ConnectionStrings("TestConnection").ToString
                objCon = New SqlConnection(_ConString)
                objCommand = New SqlCommand("SELECT Person.URN, Car.URN FROM Person INNER JOIN Car ON Person.URN = Car.URN AND PersonID=1")
                objCommand.Connection = objCon
                objCon.Open()
                objDR = objCommand.ExecuteReader(ConnectionState.Closed)
                Do While objDR.Read
                    id = objDR("URN") 'line 19
                Loop
                objDR.Close()
            Catch ex As Exception
                Throw
            Finally

            End Try

        End Sub


End Class

Please see line 19. Is it possible to do something similar to this:

objDR("Person.URN")

When I do: objDR("URN") it returns the CarURN and not the Person URN. I realise that one solution would be to use the SQL AS keyword ie:

SELECT Person.URN As PersonURN, Car.URN AS CarURN FROM Person INNER JOIN Car ON Person.URN = Car.URN AND PersonID=1

and then: objDR("PersonURN")

However, I want to avoid this if possible because of the way the app is designed ie it would involve a lot of hard coding.

Answer 1

You can look up the column by index, rather than by name. Either of the following would work:

id = objDR(0)
id = objDR.GetInt32(0)

Otherwise, your best bet is the "As" keyword or double-quotes (which are the ansi standard) to create an alias.

Answer 2

In your case, becuase of the inner join, you do not need to include both in the select clause, as equality is required, so only include either one.

So either

SELECT Person.URN 
FROM   Person INNER JOIN 
       Car ON Person.URN = Car.URN AND PersonID=1

or

SELECT Car.URN 
FROM   Person INNER JOIN 
       Car ON Person.URN = Car.URN AND PersonID=1

Answer 3

如果您已经在更改查询，并且由于某种原因无法更改其他代码，则可以根据需要创建包含列名的视图，然后从该视图中进行选择。