VB.net SUM：错误索引超出了数组的范围

Question

I have a problem with the SQL SUM function

The error I got:

Index was outside the bounds of the array.

My code:

SQLcmd = New SqlCommand("SELECT SUM(CAST(distance AS Numeric(10, 1))) FROM route WHERE id BETWEEN '" & op.departure_id & "'AND '" & op.arrival_id & "'", SQLCon)

Dim r As SqlDataReader = SQLcmd.ExecuteReader

    While r.Read()
        distance = r(3).ToString()
    End While

The error is on the distance = r(3).ToString()

Answer 1

This query selects a single column - SUM(CAST(distance AS Numeric(10, 1))) . You should access it with index 0 , not 3 :

While r.Read()
    distance = r(0).ToString()
    ' Use distance somehow...
End While