Generating the Next Id when Id is non-AutoNumber - sql

Question

I have a table called Employee. The EmpId column serves as the primary key. In my scenario, I cannot make it AutoNumber.
What would be the best way of generating the the next EmpId for the new row that I want to insert in the table?
I am using SQL Server 2008 with C#.
Here is the code that i am currently getting, but to enter Id's in key value pair tables or link tables (m*n relations)
Create PROCEDURE [dbo].[mSP_GetNEXTID]
#NEXTID int out,
#TABLENAME varchar(100),
#UPDATE CHAR(1) = NULL
AS
BEGIN
DECLARE #QUERY VARCHAR(500)
BEGIN
IF EXISTS (SELECT LASTID FROM LASTIDS WHERE TABLENAME = #TABLENAME and active=1)
BEGIN
SELECT #NEXTID = LASTID FROM LASTIDS WHERE TABLENAME = #TABLENAME and active=1
IF(#UPDATE IS NULL OR #UPDATE = '')
BEGIN
UPDATE LASTIDS
SET LASTID = LASTID + 1
WHERE TABLENAME = #TABLENAME
and active=1
END
END
ELSE
BEGIN
SET #NEXTID = 1
INSERT INTO LASTIDS(LASTID,TABLENAME, ACTIVE)
VALUES(#NEXTID+1,#TABLENAME, 1)
END
END
END

Answer 1

Using MAX(id) + 1 is a bad idea both performance and concurrency wise.
Instead you should resort to sequences which were design specifically for this kind of problem.
CREATE SEQUENCE EmpIdSeq AS bigint
START WITH 1
INCREMENT BY 1;
And to generate the next id use:
SELECT NEXT VALUE FOR EmpIdSeq;
You can use the generated value in a insert statement:
INSERT Emp (EmpId, X, Y)
VALUES (NEXT VALUE FOR EmpIdSeq, 'x', 'y');
And even use it as default for your column:
CREATE TABLE Emp
(
EmpId bigint PRIMARY KEY CLUSTERED
DEFAULT (NEXT VALUE FOR EmpIdSeq),
X nvarchar(255) NULL,
Y nvarchar(255) NULL
);
Update: The above solution is only applicable to SQL Server 2012+. For older versions you can simulate the sequence behavior using dummy tables with identity fields:
CREATE TABLE EmpIdSeq (
SeqID bigint IDENTITY PRIMARY KEY CLUSTERED
);
And procedures that emulates NEXT VALUE:
CREATE PROCEDURE GetNewSeqVal_Emp
#NewSeqVal bigint OUTPUT
AS
BEGIN
SET NOCOUNT ON
INSERT EmpIdSeq DEFAULT VALUES
SET #NewSeqVal = scope_identity()
DELETE FROM EmpIdSeq WITH (READPAST)
END;
Usage exemple:
DECLARE #NewSeqVal bigint
EXEC GetNewSeqVal_Emp #NewSeqVal OUTPUT
The performance overhead of deleting the last inserted element will be minimal; still, as pointed out by the original author, you can optionally remove the delete statement and schedule a maintenance job to delete the table contents off-hour (trading space for performance).
Adapted from SQL Server Customer Advisory Team Blog.
Working SQL Fiddle

Answer 2

The above
select max(empid) + 1 from employee
is the way to get the next number, but if there are multiple user inserting into the database, then context switching might cause two users to get the same value for empid and then add 1 to each and then end up with repeat ids. If you do have multiple users, you may have to lock the table while inserting. This is not the best practice and that is why the auto increment exists for database tables.

Answer 3

I hope this works for you. Considering that your ID field is an integer
INSERT INTO Table WITH (TABLOCK)
(SELECT CASE WHEN MAX(ID) IS NULL
THEN 1 ELSE MAX(ID)+1 END FROM Table), VALUE_1, VALUE_2....

Answer 4

Try following query
INSERT INTO Table VALUES
((SELECT isnull(MAX(ID),0)+1 FROM Table), VALUE_1, VALUE_2....)
you have to check isnull in on max values otherwise it will return null in final result when table contain no rows .