SQL Server: auto-generated custom format sequence number

Question

I am working with Microsoft SQL Server 2014. In our requirement, custom formatted sequence number is include.

The sequence number format is CAT-YYYY-MM-NNNNNN. Sample data:

CAT-2016-10-000001
CAT-2016-10-000002
                 .
                 .
                 .
CAT-2016-10-999999

I don't want to use GUID or any other and I want to work with a procedure or function.

So, I am trying with this:

CREATE TABLE [category]
(
    [id] int NOT NULL UNIQUE IDENTITY,
    [category_no] nvarchar(20) NOT NULL,
    [category_name] nvarchar(50) NOT NULL,
    PRIMARY KEY ([id])
);

CREATE FUNCTION generate_category_no() 
RETURNS CHAR(20) 
AS 
BEGIN 
    DECLARE @category_no CHAR(20) 
    SET @category_no = (SELECT MAX(category_no) FROM category) 

    IF @category_no IS NULL
         SET @category_no = 'CAT-' + YEAR(getDate()) + '-' + MONTH(getDate()) + '-000001' 

    DECLARE @no int 
    SET @no = RIGHT(@category_no,6) + 1 

    RETURN 'CAT-' + YEAR(getDate()) + '-' + MONTH(getDate()) + '-' + right('00000' + CONVERT(VARCHAR(10),@no),6) 
END
GO

ALTER TABLE category DROP COLUMN category_no;
ALTER TABLE category ADD category_no AS dbo.generate_category_no();

INSERT INTO category (category_name) 
VALUES ('BMW'), ('JAGUAR');

When I run the above SQL in step-by-step, it is OK. It shown no error. But when I run the following command:

SELECT * FROM category;

it shows the following error:

Msg 217, Level 16, State 1, Line 1
Maximum stored procedure, function, trigger, or view nesting level exceeded (limit 32).

I don't know how to solve this one. And even I don't know my function has worked or not. I referenced from internet for this function.

ADDED

I need to reset sequence no for every month. Eg. for next month, no should be as follow:

CAT-2016-11-000001

Please, enlighten me. Thanks in advance!

Answer 1

Finally, I solved the problem. My Function look like as follow:

CREATE FUNCTION generate_category_no() 
RETURNS CHAR(20) 
AS 
BEGIN 
    DECLARE @category_no CHAR(20) 
    SET @category_no = (SELECT MAX(category_no) FROM category WHERE category_no LIKE CONCAT('CAT-', YEAR(getDate()), '-', MONTH(getDate()), '-%')) 
    IF @category_no is null SET @category_no = CONCAT('CAT-', YEAR(getDate()), '-', MONTH(getDate()), '-000000')
    DECLARE @no INT 
    SET @no = RIGHT(@category_no,6) + 1 
    RETURN CONCAT('CAT-', YEAR(getDate()), '-', MONTH(getDate()), '-', RIGHT('00000' + CONVERT(VARCHAR(10),@no),6))
END
GO

And I insert data as follow:

INSERT INTO category (category_no, category_name) VALUES (dbo.generate_category_no(),'BMW');
INSERT INTO category (category_no, category_name) VALUES (dbo.generate_category_no(),'JAGUAR');

One things is that We can call function from INSERT query.

So, when I run the following sql:

SELECT * FROM category;

It give the result as shown in below.

+---+--------------------+--------------+
|id |category_no         |category_name |
+---+--------------------+--------------+
| 1 |CAT-2016-10-000001  | BMW          |
| 2 |CAT-2016-10-000002  | JAGUAR       |
+---+--------------------+--------------+

Thanks everybody for helping me. Thanks!!!