How to generate a range of dates in SQL Server

The title doesn't quite capture what I mean, and this may be a duplicate.

Here's the long version: given a guest's name, their registration date, and their checkout date, how do I generate one row for each day that they were a guest?

Ex: Bob checks in 7/14 and leaves 7/17. I want

('Bob', 7/14), ('Bob', 7/15), ('Bob', 7/16), ('Bob', 7/17)

as my result.

Thanks!

I would argue that for this specific purpose the below query is about as efficient as using a dedicated lookup table.

DECLARE @start DATE, @end DATE;
SELECT @start = '20110714', @end = '20110717';

;WITH n AS 
(
  SELECT TOP (DATEDIFF(DAY, @start, @end) + 1) 
    n = ROW_NUMBER() OVER (ORDER BY [object_id])
  FROM sys.all_objects
)
SELECT 'Bob', DATEADD(DAY, n-1, @start)
FROM n;

Results:

Bob     2011-07-14
Bob     2011-07-15
Bob     2011-07-16
Bob     2011-07-17

Presumably you'll need this as a set, not for a single member, so here is a way to adapt this technique:

DECLARE @t TABLE
(
    Member NVARCHAR(32), 
    RegistrationDate DATE, 
    CheckoutDate DATE
);

INSERT @t SELECT N'Bob', '20110714', '20110717'
UNION ALL SELECT N'Sam', '20110712', '20110715'
UNION ALL SELECT N'Jim', '20110716', '20110719';

;WITH [range](d,s) AS 
(
  SELECT DATEDIFF(DAY, MIN(RegistrationDate), MAX(CheckoutDate))+1,
    MIN(RegistrationDate)
    FROM @t -- WHERE ?
),
n(d) AS
(
  SELECT DATEADD(DAY, n-1, (SELECT MIN(s) FROM [range]))
  FROM (SELECT ROW_NUMBER() OVER (ORDER BY [object_id])
  FROM sys.all_objects) AS s(n)
  WHERE n <= (SELECT MAX(d) FROM [range])
)
SELECT t.Member, n.d
FROM n CROSS JOIN @t AS t
WHERE n.d BETWEEN t.RegistrationDate AND t.CheckoutDate;
----------^^^^^^^ not many cases where I'd advocate between!

Results:

Member    d
--------  ----------
Bob       2011-07-14
Bob       2011-07-15
Bob       2011-07-16
Bob       2011-07-17
Sam       2011-07-12
Sam       2011-07-13
Sam       2011-07-14
Sam       2011-07-15
Jim       2011-07-16
Jim       2011-07-17
Jim       2011-07-18
Jim       2011-07-19

As @Dems pointed out, this could be simplified to:

;WITH natural AS 
(
  SELECT ROW_NUMBER() OVER (ORDER BY [object_id]) - 1 AS val 
  FROM sys.all_objects
) 
SELECT t.Member, d = DATEADD(DAY, natural.val, t.RegistrationDate) 
  FROM @t AS t INNER JOIN natural 
  ON natural.val <= DATEDIFF(DAY, t.RegistrationDate, t.CheckoutDate);

I usually do this with a trick using row_number() on some table. So:

select t.name, dateadd(d, seq.seqnum, t.start_date)
from t left outer join
     (select row_number() over (order by (select NULL)) as seqnum
      from t
     ) seq
     on seqnum <= datediff(d, t.start_date, t.end_date)

The calculation for seq goes pretty fast, since no calculation or ordering is required. However, you need to be sure the table is big enough for all time spans.

If you have a "Tally" or "Numbers" table, life get's real simple for things like this.

 SELECT Member, DatePresent = DATEADD(dd,t.N,RegistrationDate)
   FROM @t 
  CROSS JOIN dbo.Tally t
  WHERE t.N BETWEEN 0 AND DATEDIFF(dd,RegistrationDate,CheckoutDate)
;

Here's how to build a "Tally" table.

--===================================================================
--      Create a Tally table from 0 to 11000
--===================================================================
--===== Create and populate the Tally table on the fly.
 SELECT TOP 11001
        IDENTITY(INT,0,1) AS N
   INTO dbo.Tally
   FROM Master.sys.ALL_Columns ac1
  CROSS JOIN Master.sys.ALL_Columns ac2
;
--===== Add a CLUSTERED Primary Key to maximize performance
  ALTER TABLE dbo.Tally
    ADD CONSTRAINT PK_Tally_N 
        PRIMARY KEY CLUSTERED (N) WITH FILLFACTOR = 100
;
--===== Allow the general public to use it
  GRANT SELECT ON dbo.Tally TO PUBLIC
;
GO

For more information on what a "Tally" table is in SQL and how it can be used to replace While loops and the "Hidden RBAR" of reursive CTEs that count, please see the following article.

http://www.sqlservercentral.com/articles/T-SQL/62867/

How to generate a range of dates in SQL Server

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