Updating record reference number using the previous record's reference number

I have the table below in SQL Server 2005:

id  reference  record_id
1   1234-4413   1
2   1234-0d33   1
3   NULL        1
4   1234-0d18   1
5   aaa         1
6   1234-3913   1
7   1234-4223   1

If there is not a one in the record_set field, then that field need's the previous record's reference number.

i.e. record 5 does not have a 1 set, therefore it needs the reference number from 4 and record_id needs to be set to two. Giving me the following, after an update:
id  reference  record_id
1   1234-4413   1
2   1234-0d33   1
3   1234-0d33   2
4   1234-0d18   1
5   1234-0d18   2
6   1234-3913   1
7   1234-4223   1

I have to update large numbers of records [400'000+], so cursors are not an option.

CREATE TABLE [dbo].[products](
	[id] [int] IDENTITY(1,1) NOT NULL,
	[reference_number] [varchar](20) NULL,
	[record_set] [varchar](2) NULL,
CONSTRAINT [PK_products] PRIMARY KEY CLUSTERED

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egxisAsked:
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RiteshShahConnect With a Mentor Commented:
it is creating problem with table variable but you can use below script, i created physical table and used the script.



--create table
CREATE TABLE [dbo].[products](
        [id] [int] IDENTITY(1,1) NOT NULL,
        [reference_number] [varchar](20) NULL,
        [record_set] [varchar](2) NULL
)
--insert records
insert into products
SELECT    '1234-4413', '1' UNION ALL
SELECT   '1234-0d33' , '1' UNION ALL
SELECT   NULL         ,'' UNION ALL
SELECT    '1234-0d18'  ,'1' UNION ALL
SELECT    'aaa'        ,'2' UNION ALL
SELECT    '1234-3913'  ,'1' UNION ALL
SELECT    '1234-4223'  ,'2'
 
--update
update products set
reference_number=(select pc.reference_number from products pc where pc.id=products.id-1) 
where products.record_set<>1
 
--select records
select * from products

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RiteshShahCommented:
have a look
update products set
reference_number=(select pc.reference_number from products pc where pc.id=products.id-1) 
where products.record_set<>1

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egxisAuthor Commented:
I tried your code and got an error?
Msg 4104, Level 16, State 1, Line 14
The multi-part identifier "pc.record_set" could not be bound.

I think my snippet below reflects my query above.


declare @t table ( id varchar(2), reference_number varchar(20), record_id varchar(2))
insert into @t values ( '1', '1234-4413', '1' )
insert into @t values ( '2', '1234-0d33', '1' )
insert into @t values ( '3', '', '' )
insert into @t values ( '4', '1234-0d18', '1' )
insert into @t values ( '5', 'aaa', '' )
insert into @t values ( '6', '1234-3913', '1' )
insert into @t values ( '7', '1234-4223', '1' )
 
update @t set
reference_number=(select pc.reference_number from @t pc where pc.id=pc.id-1) 
where pc.record_set<>1
 
select * from @t

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Scott PletcherSenior DBACommented:
Is the data such that you are CERTAIN there are no gaps in the numbers?  That makes it sooo much easier of course :-) .
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Scott PletcherSenior DBACommented:
Oh, and, I assume there could be more than one row in sequence with a missing reference.  For example, that this is possible:

1   1234-4413   1
2   1234-0d33   1
3   NULL        1
4   NULL        1
5   aaa          1
6   1234-3913   1

Or is it ALWAYS only ONE missing row in sequence?
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Scott PletcherSenior DBACommented:
Ok, assuming the ids ARE sequential, I think this UPDATE will do it:

UPDATE p
SET reference_number = baseP.reference_number,
    record_set = CAST(baseP.record_set AS int) + 1
FROM products p
INNER JOIN products baseP ON baseP.id = p.id - 1 AND
    baseP.reference_number LIKE '1%'
WHERE p.reference_number IS NULL OR p.reference_number NOT LIKE '1%'


If there could be more than 1 row in a row, then add a loop to execute the code until no "missing" reference_numbers are found:

DECLARE @forceRowcountTo1 TINYINT
SET @forceRowcountTo1 = 1

WHILE @@ROWCOUNT > 0
UPDATE p
SET reference_number = baseP.reference_number,
    record_set = CAST(baseP.record_set AS int) + 1
FROM products p
INNER JOIN products baseP ON baseP.id = p.id - 1 AND
    baseP.reference_number LIKE '1%'
WHERE p.reference_number IS NULL OR p.reference_number NOT LIKE '1%'
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egxisAuthor Commented:
@RiteshShah:
Thanks for your prompt responses, I will test tomorrow.

@ScottPletcher:
I currently have a function which performs something similar to the code you provided, but it's very sloooow. This is not a slight on your code [as I have not analysed it], but I need something lean and mean.

Which method might give me better results on if it were run on 400k+ rows?

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