SQL Server increment two tables in an update - sql

Question

First, SQL is NOT my strong point, as you'll see. I have one table that keeps track of the next item number, by some type, like so:
declare #maxs as table
(
Equip int,
NextId int
);
-- initial id values
insert into #maxs (Equip, NextId) values (400, 40);
insert into #maxs (Equip, NextId) values (500, 50);
If I create an item of type '400' then the next Id is 40, and that should be incremented to 41. In a case of a single add, that's easy enough. Our program does adds in batch, so here is my problem.
declare #t as table (Id int, Equip int, Descr varchar(20));
-- simulates the batch processing
insert into #t (Equip, Descr) values (400, 'Item 1');
insert into #t (Equip, Descr) values (400, 'Item 2');
insert into #t (Equip, Descr) values (500, 'Item 3');
-- generate the new id's in batch
UPDATE t
SET Id = (SELECT m.NextId + ROW_NUMBER() OVER (PARTITION BY t.Equip ORDER BY t.Equip))
FROM #t t
INNER JOIN #maxs m ON m.Equip = t.Equip
SELECT * FROM #t
This results in both Item 1 and Item 2 having the same Id because only 1 row is returned for 400, so ROW_NUMBER is the same for both. I need to be able to increment the NextId value in #maxs as well as update the entry in #t so that the second row that joins into the 400 value in #maxs will have the next value (almost like a x++ reference in c#). Is there a clean way to do that in SQL?
Thanks in advance.

Answer 1

Just go with JOIN and nested select
declare #t as table (Id int, Equip int, Descr varchar(20));
-- simulates the batch processing
insert into #t (Equip, Descr) values (400, 'Item 1');
insert into #t (Equip, Descr) values (400, 'Item 2');
insert into #t (Equip, Descr) values (500, 'Item 3');
-- generate the new id's in batch
UPDATE t
SET
Id = t.Equip + s.RowNum
FROM #t t
JOIN (select Equip,
Descr,
ROW_NUMBER() OVER (PARTITION BY Equip ORDER BY Equip) RowNum
from #t) s
on t.Equip = s.Equip and t.Descr = s.Descr
select * from #t
And if possible, try to switch from table variable to temporary table

Answer 2

You can do what you want with a CTE:
WITH toupdate as (
SELECT t.*,
ROW_NUMBER() OVER (PARTITION BY t.Equip ORDER BY t.Equip) as seqnum
FROM #t t
UPDATE t
SET
Id = m.NextId + seqnum
FROM toupdate t INNER JOIN
#maxs m
ON m.Equip = t.Equip;
I'm not sure this is a good idea, though. It is better to use identity columns to identify each row. There are definitely some cases, though, where numbering within a group is useful as a secondary key (for instance, line items on an invoice).