How to pass one by one column values to a SQL function?

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SQL-Server-2016

This is my table "LoadData"

Sequence_Code |     ID | Current_Year | Record_Date| Status     |
 :------------ | -----: | -----------: | :----------|          --|
 17AA          | 310001 |         2017 | 2017-01-01 | S
 18AB          | 310002 |         2018 | 2018-02-22 | A
 19AC          | 310003 |         2019 | 2019-02-10 | S
 NULL          | 310004 |         2019 | 2019-02-20 | A
 NULL          | 310005 |         2020 | 2019-03-20 | A
 NULL          | 310006 |         2020 | 2019-04-20 | A

How can we pass one by one 'ID' of only those records where Sequence_Code is NULL and Status is A

My function is "dbo.GetNextSequenceCode_TEST"

SQL

CREATE FUNCTION [dbo].[GetNextSequenceCode_TEST] (@LastSeqAlphabet varchar(50))
  RETURNS varchar(100)
   AS
    BEGIN 
	    --Will generate And Update a Sequence Code in the same table
 
	   END

Please Update the Input Parametes of the Function,If Required.

What I have tried:

I could not try,because i have no clue to do so

Posted 6-Jan-21 4:20am

Member 15036870

Updated 6-Jan-21 6:46am

Maciej Los

v2

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2 solutions

Solution 1

Try some tutorials and you will get many clues, for example: SQL CASE Statement[^]

Posted 6-Jan-21 4:55am

Richard MacCutchan

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CHill60 · Accepted Answer · 2021-01-06T05:10:00

SQL Server is set-based, so you don't pass things one-by-one to a function!

You probably need something like (untested)

SQL

UPDATE LoadData 
SET Sequence_Code = dbo.GetNextSequenceCode_TEST([ID]) 
WHERE [Status] = 'A' AND Sequence_Code IS NULL;

You also state in your function

Quote:
--Will generate And Update a Sequence Code in the same table

No it won't.

If you check the documentation [^] you will see

Quote:
UPDATE, INSERT, and DELETE statements modifying table variables that are local to the function.

Just make sure that you can work out what the next sequence number is meant to be and do the update the way I have shown above

UPDATE:
You might be tempted to something like this in your UDF

SQL

CREATE FUNCTION [GetNextSequenceCode_TEST] (@parm int)
  RETURNS varchar(100)
AS
BEGIN
	-- Get most recent Sequence_Code  
	declare @lastseqcode varchar(100)
	SELECT TOP 1 @lastseqcode = Sequence_Code FROM LoadData 
	WHERE ID < @parm AND Sequence_Code is not null
	order by ID DESC

	-- work out what the "next" one should be 
	declare @intPart char(2) = SUBSTRING(@lastseqcode, 1, 2)
	declare @charPart char(2) = SUBSTRING(@lastseqcode, 3, 2)

	-- I can't be bothered to do anything fancy here
	set @intPart = CAST(CAST(@intPart as int) + 1 AS varchar(2))
	RETURN @intPart + @charPart
END

If you do, then you will discover that all of the Sequence_Code values get set to the same value (20AC in this example). That is because the UPDATE is a single transaction, so the "previous" update isn't "visible" to the function until the entire transaction has completed on the set of data.

It's a very bad idea to do it that way for another reason - what if another user is trying to run the same function against the same table - what will the "most recent" value returned to each one? You will have essentially rendered the database single-user only, in which case why bother using SQL Server?

The body of your function should calculate the "next" sequence based on the parameter passed. It's ok to have a @LastSeqAlphabet passed in - but how are you determining what the "last" sequence was ... the comments above apply, except the impact is even worse if you query for that outside the function (more time for someone else to get in there!)