Generating a sequence in SQL

I came through one of the many interesting SQL questions on one of the forums yesterday. The original poster of the question wanted to get a list of next 15 dates from today. And he wanted to do this by using cursors. While you can write a cursor to get the results in this case, but cursor are not meant to be used like this. A cursor is used to step through the results of a query that returns multiple results e.g. rows from a table.

One good old way of generating a sequence of next n dates would be to use the WHILE loop in SQL.


DECLARE @LoopCount INT
SET @LoopCount = 0
 
DECLARE @calcDate DateTime
SET @calcDate = GETDATE() 

DECLARE @outDate varchar(30) 

WHILE @LoopCount < 15
BEGIN
 
	 SET @outDate = CONVERT(NVARCHAR, @calcDate, 103) 
	 PRINT @outDate
	 SET @calcDate = DATEADD(dd, 1, @calcDate) 

	 SET @LoopCount = @LoopCount + 1
END

Generating a sequence of dates in SQL

Another better alternative would be to use the Common Table Expressions in SQL Server.

A common table expression (CTE) can be thought of as a temporary result set that is defined within the execution scope of a single SELECT, INSERT, UPDATE, DELETE, or CREATE VIEW statement. A CTE is similar to a derived table in that it is not stored as an object and lasts only for the duration of the query. Unlike a derived table, a CTE can be self-referencing and can be referenced multiple times in the same query.


WITH q AS
	(
	SELECT  GETDATE() AS datum
	UNION ALL
	SELECT  datum + 1
	FROM    q
	WHERE datum + 1 < GETDATE() + 15
	)
SELECT  CONVERT(NVARCHAR, DATEADD(dd, DATEDIFF(dd, 0, datum), 0), 103) AS MyDate
FROM    q

Generating a sequence of numbers in SQL

Similarly, you can generate the sequence of number in SQL using the Common Table Expressions


WITH q AS
	(
	SELECT  1 AS num
	UNION ALL
	SELECT  num + 1
	FROM    q
	WHERE num < 15
	)
SELECT  * FROM    q

Generating a sequence of alphabets in SQL

Or, you can even generate the sequence of alphabets in SQL using the Common Table Expressions


WITH q AS
	(
	SELECT  0 AS num
	UNION ALL
	SELECT  num + 1
	FROM    q
	WHERE num <= 26
	)
SELECT CHAR(num + 65) FROM    q