Introduction

Generating next numbers in SQLServer should not be

a problem. But problem arises when customer ask for different types of next

numbers where you cannot generate directly from SQLServer. This brief article

describes how you would tackle this problem in different scenarios.

Number Generating Requirements

I was in a team of developing Invoicing System for a major photo

developer Sri Lanka which has Orders, Invoices and Receipts among others. When

we carried out a system study we found that their number generating is quite

different to other clients, which we have implemented. Normally others would be

happy if it is a general increment which is unique. In SQLServer there is a

property of Increment which we were using happily for some times. But for this

particular customer things were not easy.

For all numbers there should be a prefix which attached to it. It is “O”, “I”

and “R” for Orders, Invoices Receipts respectively.

Invoice number should be reset in every month while receipt number reset in

every year.

Invoice number consists of year and month while receipt number must contain year

for its number.

Order number sequence is depending on the channel wise. This client has several

channels. Channel 'A' order number has different sequence to that of channel

'B'.

There are some other source documents such as delivery orders, advance slips

where their sequence number method has not implemented at the time of the

discussion. But they said it will be one of the above methods.

These are their main requirement to the number generating. Thing are not easy as

it looks.

Implementation

As the fully implementation is not completed we had to design in advance. We

adopted the following methods of doing it.

Main steps are storing last number, reading last number and updating it.

Storing Last Number

Followings are the file structures, which are used to keep the last number.

Main Seq_no table was introduced to keep the Sequence

CREATE TABLE [dbo].[SEQ_NO] (
[TYPE] [varchar] (5) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL ,
[Prefix] [varchar] (50) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ,
[LastNumber] [int] NULL ,
[Length] [smallint] NULL ,
[Year] [bit] NULL ,
[Month] [bit] NULL ,
[LastYear] [smallint] NULL ,
[LastMonth] [smallint] NULL ,
[TableName] [varchar] (10) COLLATE SQL_Latin1_General_CP1_CI_AS NULL 
) ON [PRIMARY]
GO
Sample Data for the SEQ_NO

2. Table for keep channel wise sequence numbers

CREATE TABLE [dbo].[SEQ_CHAN] (
[Code] [nvarchar] (5) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL ,
[LastNumber] [int] NULL 
) ON [PRIMARY]
GO

Sample Data for the SEQ_CHAN

Reading and updating Last Number
I have used single stored procedure for reading and updating the last number. This is due to the fact that in multi user environment, there can be a case where two users get same number for the same record type. To avoid that at the point of generating the next number, number will be updated to the tables.
The stored procedure (sp_Get_Next_Number) has three parameters. First parameter is the type i.e. INV or ORD or RCT. The second parameter is date. Normally date is current system date. However, in the cases of generating previous document, date has to be parameterized keeping the system date as the default. Last parameter is optional parameter for the second table code.
/* Purpose :Get Last Number 
Author : PPG Dinesh Asanka
Create Date : 2002-01-23

Version Date Modification 
1.01 2002-02-28 Change to Get Last Number from Channel wise table
*/CREATE PROCEDURE [dbo].[sp_Get_Next_Number]
@TypeID as varchar(5),@TranDate as varchar(20) = "",@secondType as varchar(5) = ""
AS
DECLARE @Prefix VARCHAR(1),
@LastNumber int,
@Length smallint,
@Year bit,
@Month bit,
@LastYear smallint,
@LastMonth smallint,
@DiffrentTable bit,
@TableName varchar(10),
@TrnYear varchar(2),
@TrnMonth varchar(2),
@char_Next_Number as varchar(25),
@SQL as varchar(120),
@charLastNumber as varchar(15)

If @TranDate = "" 
Select @TranDate = GetDate()

if exists (Select * From SEQ_NO Where TYPE = @TypeID)
begin
Select @prefix = Prefix,
@LastNumber = LastNumber,
@Length = Length,
@Year = [Year],
@Month = [Month],
@LastYear = [LastYear],
@LastMonth = [LastMonth],
@DiffrentTable = [DiffrentTable],
@TableName = [TableName]
From SEQ_NO Where TYPE = @TypeID

if (@DiffrentTable = 1) 
Select @LastNumber = LastNumber From SEQ_CHAN Where CODE = @secondType

Select @LastNumber = @LastNumber + 1
-- To Fill 0 for prefix
Select @charLastNumber = RTRIM(REPLICATE("0",@length - len(@LastNumber)) + cast(@LastNumber as varchar(10)))

Select @TrnYear = RIGHT(DATEPART(yyyy, @TranDate) ,2)
Select @TrnMonth = Month( @TranDate)
If Len(@TrnMonth) = 1 Select @TrnMonth = '0' + @TrnMonth

if @Year = 1 AND @Month = 1 -- Next Number is change for Every Month
if @LastMonth = Month(@TranDate) AND @LastYear = RIGHT(DATEPART(yy, @TranDate) ,2)
Select @char_Next_Number = @TrnYear + @TrnMonth + @charLastNumber
else
begin
Select @char_Next_Number = @TrnYear + @TrnMonth + REPLICATE ("0" ,@length -1) + '1'
Select @LastNumber = 1
Select @LastMonth = @TrnMonth
Select @LastYear = @TrnYear
end
else
if @Year = 1 -- Next Number is changing for Every year
if @LastYear = RIGHT(DATEPART(yy, @TranDate) ,2)
Select @char_Next_Number = @TrnYear + @charLastNumber
else
begin 
Select @LastYear = @LastYear
Select @LastNumber = 1
Select @char_Next_Number = @TrnYear + REPLICATE ("0" ,@length -1) + '1'
end
else
Select @char_Next_Number = @charLastNumber


Select RTRIM(LTRIM(ISNULL(@prefix,"") + @char_Next_Number))

-- Update Tables for next Numbers
if (@DiffrentTable = 1) 
begin

Select @sql = "Update " + @Tablename + " Set LastNumber =" 
+ Cast(@LastNumber as varchar(10)) + 
" Where CODE ='" + @secondType + "'"
execute (@sql)
end
Update SEQ_NO Set LastNumber = @LastNumber,
LastYear = @LastYear,
LastMonth = @LastMonth
Where TYPE = @TypeID
end
else
Select "Invalid Type"

Examples

Following results will be returned for the above data set

sp_Get_Next_Number 'INV' = I04020985

sp_Get_Next_Number 'RCT' = R0000000126

sp_Get_Next_Number 'ORD','','A' = 0400009535

Limitations

Problem arises when user trying to make ad hoc changes for the existing

numbering system. Therefore, specifically we advised them not to do ad hoc

changes to the numbering method.

Conclusion

Until now, we have not found any problems with regard to the above numbering

system. Do you have any other way of doing these things? I warmly welcome any

suggestions and improvements to the above numbering system.