Toad World Blog

SQL: Different ways to generate sequence

Feb 6, 2017 12:53:13 PM by prashanthjayaram

There was a question from the op regarding adding a new column to a query output by generating the cyclic sequence numbers from 1 to 3.

Select A =identity(int,1,1),B,C from table_abs
1,A,41
2,B,13
3,C,90
4,D,91
5,E,98
6,F,12
7,G,54
8,H,16

For this output, the 4th column generates the Sequence of numbers from 1 to 3 which is shown below

1,A,41,1
2,B,13,2
3,C,90,3
4,D,91,1
5,E,98,2
6,F,12,3
7,G,54,1
8,H,16 ,2

If you are using SQL 2012 then Sequence would be natural choice for any such operations.

 

Solution 1

Using Sequence

CREATE
 SEQUENCE Seq
AS INTEGER
START WITH 1
INCREMENT BY 1
MINVALUE 1
MAXVALUE 3
CYCLE;
SELECT table_name,NEXT VALUE FOR Seq New_column
FROM information_schema.tables

 

Solution 2

Using CTE and Modulus operator

;with q as
(
select row_number() over (order by (select null)) A, *
from sys.objects
)
select A, 1+A%3 B, *
from q

 

Solution 3

Loops and Temp table

create table dummyTest
(
id int,
col1 char(1),
col2 int
)
insert into dummyTest values(1,'A',410),(2,'B',411),(3,'c',4111),(4,'d',421),(5,'e',441),(6,'f',451),(7,'g',481),(8,'h',401)

create table #dummy
(
id int,
col1 char(1),
col2 int,
NewColumn int
)
declare @n int,@i int,@limit int
set @limit=1
set @i=1
select @n=count(*) from dummyTest
while @i<=@n
begin
set @limit=1
while @limit<=3
begin
print @limit
insert into #dummy
select *,NewColumn=@limit from dummyTest where id=@i
set @i=@i+1
set @limit=@limit+1
end
end

select * from #dummy

 

Conclusion

The same solution can be derived using the cursor and there may be other solutions as well. At many instances, we opt for any solutions without thinking of data volume that may degrade the performance. This is one of the prime examples of why we need to upgrade to newer version.

Tags: SQL Server

prashanthjayaram

Written by prashanthjayaram

I’m a Database technologist having 8+ years of rich, hands-on experience on Database technologies. I am Microsoft Certified Professional and backed with a Degree in Master of Computer Application. My expertise lies in T-SQL programming, Replication and PowerShell.