Create automatic code - sql

Question

I want to create automatic code example:
B001, B002, B003, B004 .....
I have create the function for that:
CREATE FUNCTION AUTO_CODE()
RETURNS CHAR (4)
AS
BEGIN
DECLARE #KODE CHAR(4)
SELECT #KODE = COUNT (KODE_BARANG)FROM BARANG
IF #KODE>0
BEGIN
SELECT #KODE = RIGHT(KODE_BARANG,4) FROM BARANG
SET #KODE = #KODE+1
END
ELSE SET #KODE=1
RETURN 'B' + LEFT('00',3-LEN(#KODE))+(#KODE)
END
The function above only works for B001 through B010, beyond that it was back to B001. It won't work for B011, B012 or B120.
After that I have try to do with if else:
...
DECLARE KODENYA CHAR (5)
IF #KODE >= 0 AND #KODE <=9
BEGIN
SET #KODENYA = 'B' + LEFT('00',4-LEN(#KODE))+(#KODE)
END
ELSE IF #KODE >= 10 AND #KODE <=99
BEGIN
SET #KODENYA = 'B' + LEFT('0',4-LEN(#KODE))+(#KODE)
END
ELSE IF #KODE >= 100 AND #KODE <=999
BEGIN
SET #KODENYA = 'B' + LEFT('',4-LEN(#KODE))+(#KODE)
END
RETURN #KODENYA
The result is still the same and somehow I get #KODE if it was beyond 9 it return to null and SQL SERVER read it as 0.
Is there another way to create this kind of code in SQL SERVER?

Answer 1

There is no need for multiple if/case just simple FORMAT:
CREATE TABLE #tab(KODE INT);
INSERT INTO #tab(KODE) VALUES (1),(2),(10),(99),(101),(100),(999);
SELECT FORMAT(KODE, 'B00#')
FROM #tab;
LiveDemo
You can easily tweak it for longer codes by changing format string 'B000#'
And in your case:
CREATE FUNCTION [dbo].[AUTO_CODE]()
RETURNS CHAR(4)
AS
BEGIN
DECLARE #KODE INT = (SELECT COUNT(KODE_BARANG)FROM BARANG);
RETURN FORMAT(#KODE, 'B00#');
END
Warning:
You function may return duplicates/create gaps when many concurrent calls occur.
SqlFiddleDemo
Depending on your needs you may consider adding calculated column to your BARANG table:
CREATE TABLE BARANG(ID INT IDENTITY(1,1) PRIMARY KEY,
col2 VARCHAR(120) NOT NULL,
...
KODE AS (FORMAT(ID, 'B00#'))
);