Avoiding GROUP BY on specific columns - sql

Question

I am looking at avoiding grouping by specific columns in a large query to reduce performance problems.
Example: http://sqlfiddle.com/#!18/cb98e/2
CREATE TABLE [OrderTable]
(
[id] INT,
[OrderGroupID] INT,
[Total] INT,
[fkPerson] INT,
[fkitem] INT,
PRIMARY KEY (id)
)
INSERT INTO [OrderTable] (id, OrderGroupID, Total, [fkPerson], [fkItem])
VALUES ('1', '1', '20', '1', '1'),
('2', '1', '45', '2', '2'),
('3', '2', '32', '1', '1'),
('4', '2', '30', '2', '2');
CREATE TABLE [Person]
(
[id] INT,
[Name] VARCHAR(32),
PRIMARY KEY (id)
)
INSERT INTO [Person] (id, Name)
VALUES ('1', 'Fred'),
('2', 'Sam');
CREATE TABLE [Item]
(
[id] INT,
[ItemNo] VARCHAR(32),
[Price] INT,
PRIMARY KEY (id)
)
INSERT INTO [Item] (id, ItemNo, Price)
VALUES ('1', '453', '23'),
('2', '657', '34');
Query:
WITH TABLE1 AS
(
SELECT
P.ID AS [PersonID],
P.Name,
SUM(OT.[Total]) AS [Total],
i.[id] AS [ItemID],
ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) AS rownum,
ot.fkperson
FROM
OrderTable OT
INNER JOIN
Person P ON P.ID = OT.fkperson
INNER JOIN
Item I ON I.[id] = OT.[fkItem]
GROUP BY
P.ID, P.Name, i.id, ot.fkperson
)
SELECT
*,
Totalrows = (SELECT MAX(rownum) FROM TABLE1)
FROM
TABLE1
Result:
| PersonID | Name | Total | ItemID | rownum | fkperson | Totalrows |
+----------+------+-------+--------+--------+----------+-----------+
| 1 | Fred | 52 | 1 | 1 | 1 | 2 |
| 2 | Sam | 75 | 2 | 2 | 2 | 2 |
Now, for example if i didn't want to GROUP BY a varchar column (Person Name) i could do this - remove person table and join it back later. e.g.
WITH TABLE1 AS
(
SELECT
-- P.ID AS [PersonID],
-- P.Name,
SUM(OT.[Total]) AS [Total],
i.[id] AS [ItemID],
ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) AS rownum,
ot.fkperson
FROM
OrderTable OT
-- INNER JOIN Person P ON P.ID = OT.fkperson
INNER JOIN
Item I ON I.[id] = OT.[fkItem]
GROUP BY
-- P.ID, P.Name,
i.id, ot.fkperson
)
SELECT
p.id as [PersonID],
p.Name,
t1.[total],
t1.[itemid],
t1.[rownum],
t1.fkperson
-- Totalrows = (SELECT MAX(rownum) FROM TABLE1 GROUP BY
-- i.id
-- ,ot.fkperson
-- )
FROM
TABLE1 T1
INNER JOIN
Person P ON P.ID = T1.fkperson
Result:
| PersonID | Name | total | itemid | rownum | fkperson |
+----------+------+-------+--------+--------+----------+
| 1 | Fred | 52 | 1 | 1 | 1 |
| 2 | Sam | 75 | 2 | 2 | 2 |
My issue is I also want to include the MAX(rownum) column but how can I do this in my last query without having to group by everything again? What's the best approach to this? Have I missed something really obvious? :)

Answer 1

You can also use CROSS APPLY. And count for the total you can use COUNT(*) OVER()
SELECT
P.id as [PersonID],
P.Name,
T1.[total],
I.id as [itemid],
ROW_NUMBER() OVER (
ORDER BY (SELECT NULL)
) AS [rownum],
T1.fkperson,
COUNT(*) OVER () Totalrows
FROM
Item I
CROSS APPLY (SELECT ot.fkperson, SUM(OT.[Total]) AS [total]
FROM OrderTable OT
WHERE I.[id] = OT.[fkItem]
GROUP BY ot.fkperson ) AS T1
INNER JOIN Person P ON P.id = t1.fkperson
Result:
PersonID Name total itemid rownum fkperson Totalrows
----------- ----------- ----------- ----------- --------- ----------- -----------
1 Fred 52 1 1 1 2
2 Sam 75 2 2 2 2