Sql server not unique auto-increment column - sql-server

Question

Let's say I have a table called [dbo].[Order] in my MSSQL Server database like the following:
CREATE TABLE [dbo].[Order] (
[Id] INT IDENTITY (1, 1) NOT NULL,
[NumberInMonth] INT NOT NULL,
[Amount] DECIMAL (18, 2) NOT NULL,
CONSTRAINT [PK_dbo.Order] PRIMARY KEY CLUSTERED ([Id] ASC)
);
I want to have NumberInMonth column to be:
auto-incremented, so that the database will guarantee that the INSERT operation will create a new record with the value of Number = < previous value of Number > + 1 without any effort on the side of the application code
not unique, so that i could have one order #18 in January and another one order #18 in February (which will differ by Id field)
And also I'd like to have a way to have a schedulled operation which will reset the counter of NumberInMonth every first day of a month
How do I achieve it?

Answer 1

A simple sequence can provide the auto-incrementing functionallity:
CREATE SEQUENCE seq_numberInMonth as int START WITH 1 INCREMENT BY 1;
CREATE TABLE [dbo].[Order] (
[Id] INT IDENTITY (1, 1) NOT NULL,
[NumberInMonth] INT NOT NULL DEFAULT(next value for seq_numberInMonth),
[Amount] DECIMAL (18, 2) NOT NULL,
CONSTRAINT [PK_dbo.Order] PRIMARY KEY CLUSTERED ([Id] ASC)
);
Test:
INSERT INTO [Order] (Amount) VALUES (12.0), (13.0), (14.0)
SELECT *
FROM [Order]
results:
Id NumberInMonth Amount
1 1 12,00
2 2 13,00
3 3 14,00
You can quite easily create a scheduled job to run every 1st of the month and reset the sequence:
ALTER SEQUENCE seq_numberInMonth RESTART WITH 1 ;
Creating the job in t-sql can be done like this: (didn't test it, but it should work according to the following links):
How to: Create a SQL Server Agent Job
Create a Job
USE msdb ;
GO
EXEC dbo.sp_add_job
#job_name = N'seq_numberInMonth reset' ;
GO
EXEC sp_add_jobstep
#job_name = N'seq_numberInMonth reset',
#step_name = N'1st',
#subsystem = N'TSQL',
#command = N'ALTER SEQUENCE seq_numberInMonth RESTART WITH 1 ;',
#retry_attempts = 5,
#retry_interval = 5 ;
GO
EXEC sp_add_schedule #schedule_name = 'every 1st of the month'
, #enabled = 1
, #freq_type = 16
, #freq_interval = 1
GO
EXEC sp_attach_schedule
#job_name = N'seq_numberInMonth reset',
#schedule_name = N'every 1st of the month';
GO
EXEC dbo.sp_add_jobserver
#job_name = N'seq_numberInMonth reset';
GO