SQLServerCentral Article

Sequential Numbering


Microsoft SQL server does not support a method of identifying the row numbers

for records stored on disk, although there are a number of different techniques

to associate a sequential number with a row. You might want to display a set of

records might where each record is listed with a generated number that

identifies the records position relative to the rest of the records in the set.

The numbers might be sequential that start at 1 and are incremented by 1 for

each following record, like 1,2,3,4, etc.. Or in other case you may want to

sequentially number groupings of records where each specific set of records are

numbered starting at 1 and incremented by 1 until the next set is reach where

the sequence starts over. This article will show a number of different methods

of assigning a record sequence number to records returned from a query.

Sequentially Numbering Records By Having an Identity Column

Even though Microsoft SQL Server does not physically have a row number stored

with each record, you can include one of your own. To have your own record

number, all you need to do is include an identity column in your table

definition. When you define the identity column you can specify an initial seed

value of 1, and a increment value of 1. By doing this the identity column will

sequentially number each row inserted into the table. Let me show you a simple

CREATE TABLE statement that defines a ROW_NUMBER column, which will sequentially

number records.


When you run this code it produces the following output:

------------- ---------------------------------------- 

Now as you can see, each record has been automatically numbered using the

identity column RECORD_NUMBER. One thing to consider when using this method is

that there is no guarantee that these numbers are physically stored next to each

other on disk, unless there is a clustered index on the RECORD_NUMBER column. If

you use this method either create a clustered index, or have an ORDER BY

RECORD_NUMBER clause to ensure that the records are returned in sequential

order. Also remember if you should delete records, then your sequential number

will have missing values for each record deleted.

Sequentially Numbering Records by Using a Temporary Table

Now you might not have designed your table to have an identity column, or

even want to place one on your existing table, so another option is to insert

the records you desired to have a sequence number into a temporary table. Here

is some code that takes the Northwind.dbo.Employees table and copies only the

Sales Representatives into a temporary table. This example uses this temporary

table with a rank identity column to show a ranking of Sales Representatives by


create table #HireDate (rank int identity, 
HireDate datetime,
LastName nvarchar(20),
FirstName nvarchar(20)
insert into #HireDate (HireDate, LastName, FirstName)
select Hiredate, LastName, Firstname
from northwind.dbo.employees
where Title = 'Sales Representative'
order by HireDate
Select cast(rank as char(4)) as Rank, 
cast(hiredate as varchar(23)) as HireDate,
FirstName from #HireDate
Drop table #HireDate

The output of this example looks like this:

Rank HireDate LastName FirstName 
---- ----------------------- -------------------- --------------- 
1 Apr 1 1992 12:00AM Leverling Janet
2 May 1 1992 12:00AM Davolio Nancy
3 May 3 1993 12:00AM Peacock Margaret
4 Oct 17 1993 12:00AM Suyama Michael
5 Jan 2 1994 12:00AM King Robert
6 Nov 15 1994 12:00AM Dodsworth Anne

Sequentially Numbering Records by Altering Table

Ok, so you don’t want to create a temporary table, but instead you want to

use the existing table to identify the row numbers for each record. You can

still do this provided you don’t have a problem with altering the table. To have

row numbers, all you need to do is alter the table to add an identity column

with a initial seed value of 1 and an increment of 1. This will number your rows

from 1 to N where N is the number of rows in the table. Lets look at an example

of this method using the pub.dbo.titles table.

set nocount on
alter table pubs.dbo.titles
add rownum int identity(1,1)
select rownum, title from pubs.dbo.titles
where rownum < 6
order by rownum
alter table pubs.dbo.titles
drop column rownum

Note this example first alters the table, then displays the first 5 rows, and

lastly drops the identity column. This way the row numbers are produced,

displayed and finally removed, so in effect the table is left as it was prior to

running the script. The output from the above script would look like this.

rownum title 
----------- ---------------------------------------------------------------- 
1 But Is It User Friendly?
2 Computer Phobic AND Non-Phobic Individuals: Behavior Variations
3 Cooking with Computers: Surreptitious Balance Sheets
4 Emotional Security: A New Algorithm
5 Fifty Years in Buckingham Palace Kitchens

Sequentially Numbering Records by Using a Self Join

Now say your table does not have an identify column, you don’t want to use a

temporary table or alter your existing table, but you still would like to have a

record number associated with each record. In this case you could use a self

join to return a record number for each row. Here is an example that calculates

a RecNum column, and displays the LastName for each record in the

Northwind.dbo.Employees table. This example uses count(*) to count the number of

records that are greater than or equal LastName in this self join.

SELECT count(*) RecNum,
FROM Northwind.dbo.Employees a join
Northwind.dbo.Employees b
on a.LastName >= b.LastName
group by a.LastName
order by a.LastName

The results from this query looks like this:

RecNum LastName 
----------- -------------------- 
1 Buchanan
2 Callahan
3 Davolio
4 Dodsworth
5 Fuller
6 King
7 Leverling
8 Peacock
9 Suyama

This method works good for a small number of records, a few hundred or less.

Since the number of records counts produced by a self join can grows quite big

when large sets are involved, causing the performance of this technique to have

a slow response times for large set. This method also does not work if there are

duplicate values in the columns used in the self join. If there are duplicates

then the RecNum column will contain missing values.

Sequentially Number Records by Using a Cursor

A cursor can be used to associate a sequential number with records. To use

this method you would allocate a cursor, then process through each cursor record

one at a time associating a record number with each record. Here is an example

that does just that. This example displays the authors last and first name with

a calculated recnum value for each author in the pubs.dbo.authors table where

the authors last name is less than ‘G’. Each author is displayed in order by

last name and first name with the first author alphabetically being assigned a

recnum of 1, and for each successive author the recnum is incremented by one.

declare @i int
declare @name varchar(200)
declare authors_cursor cursor
for select rtrim(au_lname) + ', ' + rtrim(au_fname) from pubs.dbo.authors
where au_lname < 'G' 
order by au_lname, au_fname
open authors_cursor
fetch next from authors_cursor into @name
set @i = 0
print 'recnum name'
print '------ -------------------------------'
while @@fetch_status = 0
set @i = @i + 1
print cast(@i as char(7)) + rtrim(@name)
fetch next from authors_cursor into @name
close authors_cursor
deallocate authors_cursor

Output from the cursor query looks like this.

RecNum Name
------ -------------------------------
1 Bennet, Abraham
2 Blotchet-Halls, Reginald
3 Carson, Cheryl
4 DeFrance, Michel
5 del Castillo, Innes
6 Dull, Ann

Sequentially Numbering Groups of Records

Another case I have run across for sequentially number records, is where you

want to number groups of records. Where each group starts numbering from 1 to N,

where N is the number of records in the group, and then starts over again from

1, when the next group is encountered.

For an example of what I am talking about, lets say you have a set of order

detail records for different orders, where you want to associate a line number

with each order detailed record. The line number will ranges from 1 to N, where

N is the number of order detail records per order. The following code produces

line numbers for orders in the Northwind Order Detail table.

select OD.OrderID, LineNumber, OD.ProductID, UnitPrice, Quantity, Discount 
from Northwind.dbo.[Order Details] OD
(select count(*) LineNumber, 
a.OrderID, a.ProductID
from Northwind.dbo.[Order Details] A join
Northwind.dbo.[Order Details] B 
on A.ProductID >= B.ProductID
and A.OrderID = B.OrderID
group by A.OrderID, A.ProductID) N
on OD.OrderID= N.OrderID and 
OD.ProductID = N.ProductID
where OD.OrderID < 10251
order by OD.OrderID, OD.ProductID

This code is similar to the prior self join example, except this code

calculates the LineNumber as part of a subquery. This way the LineNumber

calculated in the subquery can be joined with the complete Order Detail record.

The above query produces the following output:

OrderID LineNumber ProductID UnitPrice Quantity Discount 
----------- ----------- ----------- --------------------- -------- --------------- 
10248 1 11 14.0000 12 0.0
10248 2 42 9.8000 10 0.0
10248 3 72 34.8000 5 0.0
10249 1 14 18.6000 9 0.0
10249 2 51 42.4000 40 0.0
10250 1 41 7.7000 10 0.0
10250 2 51 42.4000 35 0.15000001
10250 3 65 16.8000 15 0.15000001


These examples represent a number of different approaches at sequentially

numbering a sets for records. None of these methods are perfect. But hopefully

these methods will give you some ideas on how you might be able to tackle your

sequential record numbering issues


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