It appears I have a case I can't quite wrap my brains around. So coming here in hopes to find pointers to a query that maybe could be helpful to someone else too.
In the following, I have a query that functions correctly as far returning results goes but requires a second query that is the same as the one presented here but without
OFFSET and the output is just a
COUNT(*) of all of the rows.
I have two objectives:
- Write the query so that
COUNT(*)is returned in the same query. Indeed I have been looking at help pieces such as the excellent SQL SERVER – How to get total row count from OFFSET / FETCH NEXT (Paging) with different ways of solving the problem, but then there's another piece...
- Rewrite the join with a window function (e.g.
OVER(PARTITION BY) or some more performant way as that query seem to generate an
INDEX SEEKon the table. The real query is a bit more complicated in the
WHEREpart, but it looks to me even one scan could be enough if the query were a bit more straightforward so that the
MAXcould be had simultaneously with the outer query. Even this would be a win, but combined with having the overall
COUNTwould be even bigger.
Maybe I'm trying to chew a teeny bit more than I can chew currently, but on the other hand, maybe there is now a chance to learn something.
Here are the table and data
CREATE TABLE Temp ( Id INT NOT NULL PRIMARY KEY, Created INT NOT NULL, ParentId INT, SomeInfo INT NOT NULL, GroupId INT NOT NULL CONSTRAINT FK_Temp FOREIGN KEY(ParentId) REFERENCES Temp(Id) ); -- Some root levels nodes. INSERT INTO Temp VALUES(1, 1, NULL, 1, 1); INSERT INTO Temp VALUES(2, 2, NULL, 2, 2); INSERT INTO Temp VALUES(3, 3, NULL, 1, 3); INSERT INTO Temp VALUES(13, 13, NULL, 1, 1); -- First order child nodes. INSERT INTO Temp VALUES(4, 4, 1, 2, 1); INSERT INTO Temp VALUES(5, 5, 2, 1, 2); INSERT INTO Temp VALUES(6, 6, 3, 2, 3); -- Second order child nodes. INSERT INTO Temp VALUES(7, 7, 4, 1, 1); INSERT INTO Temp VALUES(8, 8, 5, 2, 2); INSERT INTO Temp VALUES(9, 9, 6, 1, 3); SELECT Id, newestTable.SomeInfo, newestTable.Created, CASE WHEN newestTable.RootCount > 1 THEN 1 ELSE 0 END AS IsMulti FROM Temp as originalTable INNER JOIN ( SELECT SomeInfo, Max(Created) AS Created, Count(*) AS RootCount FROM Temp WHERE ParentId IS NULL AND GroupId = 1 GROUP BY SomeInfo ) AS newestTable ON originalTable.SomeInfo = newestTable.SomeInfo AND originalTable.Created = newestTable.Created /*WHERE ( originalTable.SomeInfo = 1 )*/ ORDER BY newestTable.Created ASC OFFSET 0 ROWS FETCH NEXT 5 ROWS ONLY;
It looks like
SELECT Id, SomeInfo, GroupId, ParentId, MAX(Created) OVER(PARTITION BY SomeInfo) AS Created, COUNT(Id) OVER(PARTITION BY SomeInfo) AS RootCount, CASE WHEN COUNT(Id) OVER(PARTITION BY SomeInfo) > 1 THEN 1 ELSE 0 END AS IsMulti FROM Temp WHERE ( GroupId = 1 AND ParentId IS NULL ) ORDER BY Created ASC OFFSET 0 ROWS FETCH NEXT 5 ROWS ONLY;
gets close to there. The problem is, though, there are now two result rows and it appears to me this is due to the original
INNER JOIN joining back to
Temp that cull it to one row. I wonder if there is a way to apply the conditions somehow either before or after the windowing to match more closely the original query. (And this isn't the same query, to be clear. There's just so little data, hence the queries look like being close to each other.)