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Obtaining a Single Value from a Database

  • Artikkeli

You may need to return database information that is simply a single value rather than in the form of a table or data stream. For example, you may want to return the result of an aggregate function such as COUNT(*), SUM(Price), or AVG(Quantity). The Command object provides the capability to return single values using the ExecuteScalar method. The ExecuteScalar method returns, as a scalar value, the value of the first column of the first row of the result set.

The following code example inserts a new value in the database using a SqlCommand. The ExecuteScalar method is used to return the identity column value for the inserted record.

public static int AddProductCategory(string newName, string connString)
{
    var newProdID = 0;
    const string sql =
        "INSERT INTO Production.ProductCategory (Name) VALUES (@Name); "
        + "SELECT CAST(scope_identity() AS int)";
    using (SqlConnection conn = new(connString))
    {
        SqlCommand cmd = new(sql, conn);
        cmd.Parameters.Add("@Name", SqlDbType.VarChar);
        cmd.Parameters["@name"].Value = newName;
        try
        {
            conn.Open();
            newProdID = (int)cmd.ExecuteScalar();
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message);
        }
    }
    return newProdID;
}

Public Function AddProductCategory( _
  ByVal newName As String, ByVal connString As String) As Integer
    Dim newProdID As Int32 = 0
    Dim sql As String = _
     "INSERT INTO Production.ProductCategory (Name) VALUES (@Name); " _
       & "SELECT CAST(scope_identity() AS int);"

    Using conn As New SqlConnection(connString)
        Dim cmd As New SqlCommand(sql, conn)
        cmd.Parameters.Add("@Name", SqlDbType.VarChar)
        cmd.Parameters("@Name").Value = newName
        Try
            conn.Open()
            newProdID = Convert.ToInt32(cmd.ExecuteScalar())
        Catch ex As Exception
            Console.WriteLine(ex.Message)
        End Try
    End Using

    Return newProdID
End Function

See also