Question

I need to run a loop in SQL. Google this is a little hard for some odd reason. In SQL Server I just put this is in the query editor in SQL Server Managment Studio

DECLARE @z_start INT
SET @z_start = 0
DECLARE @z_end INT
SET @z_end = 0

WHILE (@z_start <= 14) BEGIN
    IF(@z_start != 0 AND @z_end != 14)
        WHILE (@z_end <= 14) BEGIN
            INSERT INTO [campusMap].[dbo].[zoom_levels] ([zoom_start],[zoom_end]) VALUES (@z_start,@z_end)
            SET @z_end = @z_end + 1
        END
        SET @z_start = @z_start + 1
    END
END

All I want to do is to set the zoom_start and zoom_end so (0,0) to (14,14) skipping only (0,14) as that is already in the table.

I think I’m close. Anyone know where it’s off? Thank you.
Cheers -Jeremy

Answer 1

Instead of doing a nested loop and inserted each row at a time, you can use a CTE (Or a pre-existing numbers table) and add all the rows you need at once:

;WITH Numbers (Number) AS 
(
    SELECT 0 
    UNION ALL
    SELECT 1 + Number FROM Numbers 
    WHERE 1 + Number <= 14
)
INSERT INTO [campusMap].[dbo].[zoom_levels] ([zoom_start],[zoom_end])
SELECT n1.Number, n2.Number 
FROM
    Numbers n1 CROSS JOIN
    Numbers n2
WHERE
    NOT (n1.Number = 0 AND n2.Number = 14)

Set-based operations in SQL are usually cleaner and easier to understand than procedural, row-by-row approaches.