How to delete rows after the item which equals to exact value? - sql

Question

I have the following dataframe
Block_id step name
1 1 Marie
1 2 Bob
1 3 John
1 4 Lola
2 1 Alex
2 2 John
2 3 Kate
2 4 Herald
3 1 Alec
3 2 Paul
3 3 Rex
As you can see data frame is sorted by block_id and then by step. I want to delete only in one block_id everything after the row where I have name John(the row with John as well). So the desired output would be
Block_id step name
1 1 Marie
1 2 Bob
2 1 Alex
3 1 Alec
3 2 Paul
3 3 Rex

Answer 1

An updatable CTE with a cumulative conditional COUNT seems to be what you are after:
CREATE TABLE dbo.YourTable (BlockID int,
Step int,
[Name] varchar(10));
GO
INSERT INTO dbo.YourTable
VALUES(1,1,'Marie'),
(1,2,'Bob'),
(1,3,'John'),
(1,4,'Lola'),
(2,1,'Alex'),
(2,2,'John'),
(2,3,'Kate'),
(2,4,'Herald'),
(3,1,'Alec'),
(3,2,'Paul'),
(3,3,'Rex');
GO
WITH CTE AS(
SELECT COUNT(CASE [Name] WHEN 'John' THEN 1 END) OVER (PARTITION BY BlockID ORDER BY Step) AS Johns
FROM dbo.YourTable)
DELETE FROM CTE
WHERE Johns >= 1;
GO
SELECT *
FROM dbo.YourTable;
GO
DROP TABLE dbo.YourTable;

Answer 2

One method uses an updatable CTE:
with todelete as (
select t.*,
min(case when name = 'John' then step end) over (partition by block_id) as john_id
from t
)
delete from todelete
where id >= john_id;
Or, if you prefer, a correlated subquery:
delete from t
where id >= (select min(t2.id)
from t t2
where t2.blockid = t.blockid and t2.name = 'John'
);
For performance, both of these can take advantage of an index on (blockid, name, id).