1. In the name of the resources
Aggregating data
Dejan Dular
Dejan Dular s.p.

2. Thank you to our AWESOME sponsors!

3. About me Dejan Dular .NET Developer SQL Developer
Dynamics CRM specialist
IoT fan
DIY & eco maniac
Twitter: @dejandular
Mail:
LinkedIn: dejandular

4. Execution plan is your friend
Include actual execution plan (seek for seek)
Review suggested missing index – CHANGE THE NAME!
Compare client statistics
Discard results after query execution [Tools-Options-Query results-Results to grid]
Use external tools
SSMS Tools Pack
SQL Sentry Plan Explorer
SQL Server Profiler
Test hypothetical indexes WITH (STATISTICS_OLNY = 1) and AUTOPILOT

5. CTE vs @temp vs #temp SPEED CTE Like a sub-query, but more readable
No (dedicated) index or statistics
In memory, results are not cached
SQL server can choose to re-run the query
SPEED
* most of the time
Table variable
In memory*
No index or statistics
Treated as if it has one row
Can be reused
Temporary table
has statistics
can be indexed

6. Getting OVER() window functions
SELECT s.TerritoryID, p.FirstName, p.LastName, s.SalesYTD
ROW_NUMBER() OVER(PARTITION BY s.TerritoryId ORDER BY s.SalesYTD)
FROM Sales.SalesPerson s
JOIN Person.Person p ON s.BusinessEntityID = p.BusinessEntityID
ORDER
TerritoryID
FirstName
LastName
SalesYTD
Row Number 1
Pamela
Ansman-Wolfe
,13
David
Campbell
,94 2
Tete
Mensa-Annan
,20 3
Michael
Blythe
,18
Jillian
Carson
,37 4
Shu
Ito
,62
Linda
Mitchell
,55
PARTITION

7. CROSS APPLY Get these rows, use (apply) them to this set
and display the data
Like a JOIN. Same same, but different.
In most cases the same execution plan when only joining the tables
Possible to use the rowset on a table valued UDF
SELECT P.Id, P.FirstName, P.LastName, O.OrderDate, O.OrderStatus
FROM Person P
CROSS APPLY (
SELECT TOP 1 OrderDate, OrderStatus
FROM SalesOrder SO
WHERE SO.CustomerId = P.ID
ORDER BY OrderDate DESC
) O
WHERE P.zip = '94604'

8. Aggregate on the fly
How many products do we have with Tax 0%, 9% and 22% in three price ranges <100€, €, >500€?
Tax
<100€
100 – 500€
>=500€ 0%
2263
9201
11726 9%
7081
28700
36114
22%
10347
42001
52567

9. Aggregate, Then Join JOIN is slow
Aggregate if possible to get less rows, then join

10. Intervals
... WHERE Price BETWEEN 100 AND 500
What does BETWEEN x AND y mean? [x,y] | (x,y) | (x,y] | [x,y)
Sum of sales over the years in Q1
Year
Sales in Q1
2012
64422,11
2013
708132,64
2014
154322,22
2015
201678,12
2016
235213,17

11. Anti-patterns
OR between columns in different tables (T1 JOIN T2… WHERE T1.col1 = x OR T2.col2 = y)
WHERE col1 = WHEN 1 THEN 'val1' WHEN 2 then 'val2' ELSE col2

12. Simulating production environment
DBCC OPTIMIZER WHAT_IF (undocumented)
DBCC Optimizer_WhatIf (1,32) --set 32 CPUs GO
DBCC Optimizer_WhatIf (2,131072) --set 128 GB of RAM
DBCC Optimizer_WhatIf (3,64) -- 64 bit system
-- Execute query
DBCC Optimizer_WhatIf (1, 0) --clear CPU
DBCC Optimizer_WhatIf (2, 0) --clear RAM
DBCC Optimizer_WhatIf (3, 0) --clear 64 bits
SET OPTIONS
Statistics
Numbers of rows and pages in the table
Available physical memory
Number of CPUs
32bit / 64 bit
Export metadata from production database

13. Very important slide Use correct data types

14. Very important slide Use correct data types
Avoid correlated sub-queries
SELECT
T1.Column1,
Column2 = (SELECT T2.Column2
FROM T2
WHERE T2.Col2 = T1.Column2 )
FROM T1

15. Very important slide Use correct data types
Avoid correlated sub-queries
Avoid using functions within ON, WHERE or GROUP BY
Remove unnecessary tables
Foreign keys are not indexed by default
Query plan numbers are only estimations
Use query hints with caution
If you are using cursors, you have to buy me a beer!
WHERE Column1 = dbo.SomeFunction(Column2)
SELECT Car.Id
FROM Car
JOIN Service ON Car.Id = Service.CarId

16. Another important slide
Do not use query builders
Investigate execution plans, check indexes, include selected columns
Make as little scans as possible, seek is what you are looking for
Limit the size of the working data set
Only select fields you really need
WITH(NOLOCK), WITH(READPAST) or ISOLATION LEVEL READ UNCOMMITED is OK only when you know what you are doing
Configure Index and Table file partitions
Upgrade SQL server to newest version

17. while (tooSlow) { Change(); Test(); Evaluate(); }

18. Que?

19. Resources
Almost every page has at least one link in the notes section. Use it to learn more about that topic.