Change row values till first match - tsql

Question

There is a table with the following structure:
(Date, Shop, Exists, Status)
2012-10-09 Shop1 0 Trial
2012-10-23 Shop1 0 New
2012-10-30 Shop1 0 New
2012-11-13 Shop1 0 New
2012-11-27 Shop1 1 New
2012-12-11 Shop1 0 New
2012-12-18 Shop1 0 New
I need to convert it to the following result:
2012-10-09 Shop1 0 Trial
2012-10-23 Shop1 0 Trial
2012-10-30 Shop1 0 Trial
2012-11-13 Shop1 0 Trial
2012-11-27 Shop1 1 New
2012-12-11 Shop1 0 New
2012-12-18 Shop1 0 New
The algorithm is set to trial till Exists column = 1.
There are more Shops, so getting Date value (2012-11-27 in my case) for every single shop doesn't look very sane. Any clues?

Answer 1

You can get a list of all the 'New' rows before the first ShopExists date using the query below. It includes the date the shop first existed as the last column. You should be able to use the results to update your table accordingly.
select
s1.*, s2.FirstExistsDate
from
Shops s1
inner join
( select s.ShopName, MIN(ShopDate) as FirstExistsDate
from Shops s
where ShopExists = 1
group by s.ShopName
) s2 on s1.ShopName = s2.ShopName and s1.ShopDate < s2.FirstExistsDate and s1.ShopStatus = 'New'

Answer 2

If you're not supposed to order the rows except in the way they are exactly in the database then when you go to get the Row Number (you need that to help you find all rows before the row that has 1 for Exists), then you use ORDER BY (SELECT 1) when using ROW_NUMBER. It will take the rows as they are in your table and give them row numbers.
Then find the first row with 1 for Exists and store it in a variable. You can then join the temp table that has the row numbers with your original table and do the update below.
That should do it for you!
SELECT '2012-10-09' AS ShopDate, 'Shop1' AS ShopName, '0' AS ShopExists, 'Trial' AS ShopStatus INTO #Shops UNION
SELECT '2012-10-23', 'Shop1', '0', 'New' UNION
SELECT '2012-10-30', 'Shop1', '0', 'New' UNION
SELECT '2012-11-13', 'Shop1', '0', 'New' UNION
SELECT '2012-11-27', 'Shop1', '1', 'New' UNION
SELECT '2012-12-11', 'Shop1', '0', 'New' UNION
SELECT '2012-12-18', 'Shop1', '0', 'New'
SELECT s.*
, ROW_NUMBER() OVER (ORDER BY (ShopDate)) AS RowNumber
INTO #temp
FROM #Shops s
SELECT *
FROM #temp
DECLARE #RowNumber INT = (SELECT TOP 1 RowNumber FROM #temp WHERE ShopExists = 1 ORDER BY RowNumber ASC)
--SELECT *
UPDATE s SET ShopStatus = 'Trial'
FROM #temp t
JOIN #Shops s
ON s.ShopDate = t.ShopDate
AND s.ShopName = t.ShopName
AND s.ShopExists = t.ShopExists
AND s.ShopStatus = t.ShopStatus
WHERE RowNumber < #RowNumber
SELECT *
FROM #Shops
DROP TABLE #Shops
DROP TABLE #temp
This was the end result:
ShopDate ShopName ShopExists ShopStatus
2012-10-09 Shop1 0 Trial
2012-10-23 Shop1 0 Trial
2012-10-30 Shop1 0 Trial
2012-11-13 Shop1 0 Trial
2012-11-27 Shop1 1 New
2012-12-11 Shop1 0 New
2012-12-18 Shop1 0 New