Generate a receipt number in this range

How would I go about generating a unique receipt number in the following range: GA00000-GZ99999? I am not allowed to use the 'I' and 'O' letters so GI00000-GI99999 & GO00000-GO99999 would be excluded.

Ideally, I'd like to create this in T-SQL but can also do it in VB.Net. This number will be stored in SQL and I can access it prior to generating the next one. They do not have to be sequential.

Thanks.开发者_如何转开发

Create an array of all characters that are permitted as the first digit.

For any numeric receipt id n the receipt code will be G + array[n/1000000] + n % 1000000.

keep a suffix pointer. when your index wraps over 99999, increment it. Check for your special cases and exhaustion (e.g. Z).

Here's a VB.NET version to get the next sequential number, given the previous one. I think I covered all the cases.

Private Const FirstReceiptNumber As String = "GA00000"

Public Function GenerateReceiptNumber(ByVal lastNumber As String) As String

    If lastNumber.Length <> 7 Then
        Throw New ArgumentException("Incorrect length", "lastNumber")
    End If

    If lastNumber.StartsWith("G") = False Then
        Throw New ArgumentException("Incorrect start character", "lastNumber")
    End If

    Dim letterPortion As Char = lastNumber.Chars(1)

    If letterPortion < "A"c Or letterPortion > "Z"c Then
        Throw New ArgumentException("Non-letter second character", "lastNumber")
    End If

    If letterPortion = "I"c Or letterPortion = "O"c Then
        Throw New ArgumentException("Invalid second character", "lastNumber")
    End If

    Dim numericPortionString As String = lastNumber.Substring(2)
    Dim numericPortion As Integer

    If Integer.TryParse(numericPortionString, numericPortion) = False Then
        Throw New ArgumentException("Invalid numeric portion", "lastNumber")
    End If

    If numericPortion = 99999 Then
        If letterPortion = "Z"c Then
            Throw New ArgumentException("No more receipt numbers possible", "lastNumber")
        End If

        numericPortion = 0
        letterPortion = letterPortion + Chr(1)

        If letterPortion = "I"c Or letterPortion = "O"c Then
            letterPortion = letterPortion + Chr(1)
        End If
    Else
        numericPortion = numericPortion + 1
    End If

    Return String.Format("G{0}{1:00000}", letterPortion, numericPortion)

End Function

I decided to do it as the following:

CREATE FUNCTION [dbo].[fn_generateReceiptNumber]() 
RETURNS NCHAR(7)
AS
BEGIN
    -- Declare the return variable here
    DECLARE @result NCHAR(7);   
    DECLARE @prefix NCHAR(1);
    DECLARE @suffix INT;
    DECLARE @currentMax NCHAR(7);

    SELECT @currentMax = MAX(ISNULL(fp.CustomReceiptNo, 'GA00001')) FROM dbo.FinPayment fp;

    SELECT @prefix = SUBSTRING(@currentMax,2,1);
    SELECT @suffix = CAST(SUBSTRING(@currentMax,3,7) AS INT);

    IF((@suffix + 1) > 99999)
    BEGIN
        SELECT @suffix = 0;
    END
    ELSE
    BEGIN
        SELECT @suffix = @suffix + 1;
    END

    IF(@suffix = 0)
    BEGIN
        IF(@prefix = 'Z')
        BEGIN
            RETURN -1;
        END
        ELSE
        BEGIN
            IF(NCHAR(UNICODE(@prefix)+1) IN ('I', 'O'))
            BEGIN
                SELECT @prefix = NCHAR(UNICODE(@prefix)+2);
            END
            ELSE
            BEGIN
                SELECT @prefix = NCHAR(UNICODE(@prefix)+1);
            END
        END
    END

    -- Return the result of the function
    SELECT @result = NCHAR(71) + @prefix + CAST(RIGHT('00000' + RTRIM(@suffix), 5) AS NCHAR(5));
    RETURN @result;

END
GO

Thank you everyone for the input. Steve.