Developer42

2014-09-17

T-SQL: Generate Series: Getting a list of numbers in a given range.

Filed under: Microsoft, SQL Server, Technology — Tags: , , , , , , , , , — Developer42 @ 01:27

I recently came across the Postgres generate_series function whilst reading a blog post.
So far as I can tell, there’s no equivalent in T-SQL. To make up for this, I coded my own, making use of the recursive nature of common table expressions:

create function dbo.generate_series
(
	  @start bigint
	, @stop bigint
	, @step bigint = 1
	, @maxResults bigint = 0 --0 = unlimited
)
returns @results table(n bigint)
as
begin

	--avoid infinite loop (i.e. where we're stepping away from stop instead of towards it)
	if @step = 0 return
	if @start > @stop and @step > 0 return
	if @start < @stop and @step < 0 return
	
	--ensure we don't overshoot
	set @stop = @stop - @step

	--treat negatives as unlimited
	set @maxResults = case when @maxResults < 0 then 0 else @maxResults end

	--generate output
	;with myCTE (n,i) as 
	(
		--start at the beginning
		select @start
		, 1
		union all
		--increment in steps
		select n + @step
		, i + 1
		from myCTE 
		--ensure we've not overshot (accounting for direction of step)
		where (@maxResults=0 or i<@maxResults)
		and 
		(
			   (@step > 0 and n <= @stop)
			or (@step < 0 and n >= @stop)
		)  
	)
	insert @results
	select n 
	from myCTE
	option (maxrecursion 0) --sadly we can't use a variable for this; however checks above should mean that we have a finite number of recursions / @maxResults gives users the ability to manually limit this 

	--all good	
	return
	
end

Example Usage:

--check we get expected results
select * from generate_series(1, 10, default, default)
select * from generate_series(10, 5, -1, default)
select * from generate_series(1, 10, 4, default)
select * from generate_series(1, 10, default, 2)
select * from generate_series(1, 10, 4, -1)

--check we don't get results if we have "invalid" input
select * from generate_series(1, 10, 0, default)
select * from generate_series(10, 1, default, default)
select * from generate_series(10, 5, 1, default)
select * from generate_series(1, 10, -4, default)

NB: Should you wish to generate a series of dates instead of a series of numbers, check my comments here: http://stackoverflow.com/questions/1478951/generate-a-resultset-of-incrementing-dates-in-tsql/25881077#25881077

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