Nest With clause inside a select statement - sql

Question

I have a recursive query using Common Table Expressions which gets the range of dates between a start and end date
WITH T(date) AS (
SELECT #StartDate UNION ALL
SELECT DateAdd(day,1,T.date) FROM T WHERE datediff(dd,T.date , #EndDate)>0 )
SELECT date FROM T OPTION (MAXRECURSION 32767))
Is there any way for me to nest this within another select statement without creating a temporary table?
I'm looking for a statement like so
select * from (WITH T(date) AS (
SELECT #StartDate UNION ALL
SELECT DateAdd(day,1,T.date) FROM T WHERE datediff(dd,T.date , #EndDate)>0 )
SELECT date FROM T OPTION (MAXRECURSION 32767)))
join
(select * from SomeTable where MyDate between #StartDate and #EndDate)
on //Some condition
I've tried this out in SQL Server and there is an
Incorrect Syntax near WITH
error being thrown.
By definition, CTE only exists within the scope of the query. So, is it necessary that a Temporary table is necessary to store the results of the CTE or can the above scenario also work?

Answer 1

You can use multiple CTEs by separating them with a comma, e.g:
WITH T(date) AS
(
SELECT #StartDate
UNION ALL
SELECT DateAdd(day,1,T.date)
FROM T
WHERE datediff(dd,T.date , #EndDate)>0
), T2 AS
(
SELECT date
FROM T
OPTION (MAXRECURSION 32767)
)
select * from t2
join
(select * from SomeTable where MyDate between #StartDate and #EndDate)
on //Some condition
For what it's worth though, using a recursive CTE to generate a list of dates is not the best way. The best way is to have a static calendar table, failing this you can generate a set of dates on the fly as follows:
SELECT TOP (DATEDIFF(DAY, #StartDate, #EndDate) + 1)
Date = DATEADD(DAY, ROW_NUMBER() OVER(ORDER BY a.object_id) - 1, #StartDate)
FROM sys.all_objects a
CROSS JOIN sys.all_objects b;
This will be more efficient than looping through dates. For more information see:
Generate a set or sequence without loops – part 1
Generate a set or sequence without loops – part 2
Generate a set or sequence without loops – part 3

Answer 2

Create the CTE first, then select from it.
;WITH T(date) AS (
SELECT #StartDate UNION ALL
SELECT DateAdd(day,1,T.date) FROM T WHERE datediff(dd,T.date , #EndDate)>0
)
select * from T
join
(select * from SomeTable where MyDate between #StartDate and #EndDate) v
on //Some condition
OPTION (MAXRECURSION 32767)
If you're trying to create a date range, this may help : How to create a list of dates from a daterange without using a CTE