First unused number in a varchar(5) field padded with zeros - sql

Question

I have a varchar(5) field. I need find the first unused number across all records such that they begin with leading zeros. like if there is a 00001 and a 00003 I'd like the query to return 00002. Also, many of the records contain letters and look like 'G0542'. These can be ignored.
I know I'm close. This seems to work in SQL Server 2005 but not in 2008 or 2012
http://sqlfiddle.com/#!3/4016a0/1
create table b_addr ( inst_no varchar(5) Unique );
insert into b_addr (inst_no) values ('00001');
insert into b_addr (inst_no) values ('00002');
insert into b_addr (inst_no) values ('00004');
--this is the problem line
insert into b_addr (inst_no) values ('A0045');
With usedNos as(
select CAST(b_addr.inst_no AS INT) as inst
from b_addr
where b_addr.inst_no LIKE '[0-9][0-9][0-9][0-9][0-9]')
SELECT
RIGHT('00000' + CONVERT(VARCHAR(5), COALESCE(min(inst)+1, 0)),5) AS next_inst_no
from usedNos where not exists (select null from usedNos usn where usn.inst = usedNos.inst +1)
How can I structure this so it will work in sql server 2008+ as well?

Answer 1

Here is a version of your query that works:
With usedNos as (
select CAST(case when isnumeric(b_addr.inst_no) = 1
then b_addr.inst_no
end AS INT) as inst
from b_addr
)
SELECT RIGHT('00000' + CONVERT(VARCHAR(5), COALESCE(min(inst)+1, 0)),5) AS next_inst_no
from usedNos
where inst is not null and
not exists (select 1
from usedNos usn
where usn.inst = usedNos.inst +1
);
The key is the use of isnumeric() inside of case. This guarantees that the cast() is not attempted unless the value looks like a number. If it doesn't look like a number, then the result is NULL, which is filtered out in the outer where clause.
Your where clause:
where b_addr.inst_no LIKE '[0-9][0-9][0-9][0-9][0-9]'
attempts to do the same thing. However, SQL Server doesn't guarantee that the where clause is processed before the select -- which is why you are getting an unexpected error.

Answer 2

You can check whether the number you're trying to cast is a real number:
Instead of
CAST(b_addr.inst_no AS INT) as inst
Do something like
CAST(CASE WHEN ISNUMERIC(b_addr.inst_no) = 1 THEN b_addr.inst_no ELSE 0 END AS INT) as inst
It's a bit convoluted, but it works.
Demo: http://sqlfiddle.com/#!3/1aee5/6

Answer 3

here's another one using patindex instead of like.
http://sqlfiddle.com/#!6/1aee5/12
With usedNos as(
select b_addr.inst_no as inst
from b_addr
where patindex('[0-9][0-9][0-9][0-9][0-9]',b_addr.inst_no) > 0
)
SELECT
RIGHT('00000' + COALESCE(cast((min(cast(inst as int)) + 1) as varchar), '00000'),5) AS next_inst_no
from usedNos
where not exists (select null from usedNos usn where cast(usn.inst as int) = cast(usedNos.inst as int) + 1 )
--should return 00003, trying to find the first unused inst_no and padd it with zeros to make it 5 chars.

Answer 4

create table b_addr ( inst_no varchar(5) Unique );
insert into b_addr (inst_no) values ('00001');
insert into b_addr (inst_no) values ('00002');
insert into b_addr (inst_no) values ('00004');
--this is the problem line
insert into b_addr (inst_no) values ('A0045');
--Specify how many of the "next" unused numbers you want.
DECLARE #HowMany INT = 10
--Common Table Expression construct to generate sequential numbers.
;WITH
L0 AS(SELECT 1 AS c UNION ALL SELECT 1),
L1 AS(SELECT 1 AS c FROM L0 AS A, L0 AS B),
L2 AS(SELECT 1 AS c FROM L1 AS A, L1 AS B),
L3 AS(SELECT 1 AS c FROM L2 AS A, L2 AS B),
L4 AS(SELECT 1 AS c FROM L3 AS A, L3 AS B),
L5 AS(SELECT 1 AS c FROM L4 AS A, L4 AS B),
L6 AS(SELECT 1 AS c FROM L5 AS A, L5 AS B),
SequentialNumbers AS(SELECT ROW_NUMBER() OVER(ORDER BY c) AS Num FROM L6)
SELECT TOP(#HowMany) RIGHT('00000' + CAST(sn.Num AS VARCHAR), 5) AS NextNumbers
FROM SequentialNumbers sn
WHERE sn.Num NOT IN (
SELECT CAST(b_addr.inst_no AS INT) AS inst
FROM b_addr
WHERE b_addr.inst_no LIKE '[0-9][0-9][0-9][0-9][0-9]'
)