March 3, 2011 at 12:59 pm
I found a query to select nth row....
SELECT column/s FROM
(
SELECT column/s, row_number() over(ORDER BY getdate()) as r
FROM tablename
) as t
WHERE r = 4
But couldn't find any query for deletion...
Any idea ??
March 3, 2011 at 1:08 pm
smarty3010 (3/3/2011)
I found a query to select nth row....
SELECT column/s FROM
(
SELECT column/s, row_number() over(ORDER BY getdate()) as r
FROM tablename
) as t
WHERE r = 4
But couldn't find any query for deletion...
Any idea ??
DELETE t.Column
FROM
(
SELECT column/s, row_number() over(ORDER BY getdate()) as r
FROM tablename
) as t
WHERE r = 4
March 3, 2011 at 5:53 pm
try this
BEGIN TRAN test
DELETE tablename
FROM (SELECT Column
FROM
(
SELECT column/s, row_number() over(ORDER BY getdate()) as r
FROM tablename
) as t
WHERE r = 4)tmp
INNER JOIN tablename
ON tablename.column = tmp.column
COMMIT TRAN test
March 4, 2011 at 3:32 am
Using CTE, you can select, update and delete specific record(s). Pls refer the below code
create table #temp (id int)
--delete #temp
insert into #temp values(1)
insert into #temp values(2)
insert into #temp values(3)
insert into #temp values(4)
insert into #temp values(5)
select * from #temp
;with cte (id,r_num)
as(
select *,ROW_NUMBER() over(Order by getdate()) from #temp
)
delete cte where r_num = 3;
select * from #temp
;with cte (id,r_num)
as(
select *,ROW_NUMBER() over(Order by getdate()) from #temp
)
update cte set id = 1000 where r_num = 2;
select * from #temp
drop table #temp
Thanks
Gopi
March 4, 2011 at 3:55 am
It's important to note that none of these solutions will guarantee to delete the same rows as are being returned by the select statement (nor indeed is the select statement guaranteed to return the same rows each time).
Because your row number order is entirely arbitrary, a different plan could well result in different results.
My question is, why would you want to arbitrarily delete rows with no apparent logic?
March 4, 2011 at 4:16 am
HowardW (3/4/2011)
It's important to note that none of these solutions will guarantee to delete the same rows as are being returned by the select statement...
Hi Howard,
I agree with your comments about the reason for deleting the 'nth' row in no particular order, but I can't for the life of me understand what the extract above is getting at. A query like the following is guaranteed to delete the row identified as #4 (peculiar though the logic is):
DELETE E
FROM (
SELECT rn = ROW_NUMBER() OVER (ORDER BY (SELECT 0))
FROM dbo.Example
) AS E
WHERE E.rn = 4
;
Naturally, we would normally use a deterministic order by with the row number window function to identify the row or rows to delete.
Paul
Paul White
SQLPerformance.com
SQLkiwi blog
@SQL_Kiwi
March 4, 2011 at 6:15 am
Thanks a million guys !!
Tried the code by SQLkiwi and ColdCoffee (used t instead of t.column)
Worked perfectly
I am building a visual tool for managing a database.....
So a deleting a row (which a user can view and wants to delete) would be much simpler !!
March 4, 2011 at 6:53 am
SQLkiwi (3/4/2011)
HowardW (3/4/2011)
It's important to note that none of these solutions will guarantee to delete the same rows as are being returned by the select statement...Hi Howard,
I agree with your comments about the reason for deleting the 'nth' row in no particular order, but I can't for the life of me understand what the extract above is getting at. A query like the following is guaranteed to delete the row identified as #4 (peculiar though the logic is):
DELETE E
FROM (
SELECT rn = ROW_NUMBER() OVER (ORDER BY (SELECT 0))
FROM dbo.Example
) AS E
WHERE E.rn = 4
;
Naturally, we would normally use a deterministic order by with the row number window function to identify the row or rows to delete.
Paul
It's guaranteed to delete the nth row within that delete statement, but as far as I'm aware, you could run the select (which will generate one plan) and assume that the delete statement will delete the same rows. However, the delete statement could reasonably generate a different plan and delete different arbitrary rows than your original select statement did. Unless I'm misunderstanding how the optimiser works in this case and it doesn't generate a plan based on the overall query and will always generate the plan based on the sub query alone.
Hopefully the above makes sense (even if it's wrong!) 🙂
March 4, 2011 at 7:34 am
HowardW (3/4/2011)
It's guaranteed to delete the nth row within that delete statement, but as far as I'm aware, you could run the select (which will generate one plan) and assume that the delete statement will delete the same rows. However, the delete statement could reasonably generate a different plan and delete different arbitrary rows than your original select statement did. Unless I'm misunderstanding how the optimiser works in this case and it doesn't generate a plan based on the overall query and will always generate the plan based on the sub query alone. Hopefully the above makes sense (even if it's wrong!) 🙂
I see, so you were saying that running the SELECT first (and noting the row it selected) and then expecting the DELETE (with the same SELECT statement as a subquery) to delete the same row would be unsound. I agree with that of course.
I thought you were saying that the DELETE might not delete the row identified by the SELECT (when run as part of the DELETE statement). My apologies - I think I did misread what you were getting at.
Paul White
SQLPerformance.com
SQLkiwi blog
@SQL_Kiwi
March 4, 2011 at 7:40 am
SQLkiwi (3/4/2011)
I see, so you were saying that running the SELECT first (and noting the row it selected) and then expecting the DELETE (with the same SELECT statement as a subquery) to delete the same row would be unsound. I agree with that of course.I thought you were saying that the DELETE might not delete the row identified by the SELECT (when run as part of the DELETE statement). My apologies - I think I did misread what you were getting at.
Exactly. No problem, I probably wasn't being very clear! 😛
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