Window functions

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Meetup PUG
30 Aprile 2019
#AperiTech

$ docker pull mysql
$ docker start some-mysql
$ docker run -it --link some-mysql:mysql --rm mysql sh -c
'exec mysql -h"$MY...

mysql> INSERT INTO gain VALUES
('Cavalieri', '2019-03-01', 269),
('J.K.Place', '2019-02-01', 450),
('Manfredi', '2019-01-0...

$mysqli = new mysqli('127.0.0.1', 'your_user', 'your_pass', 'wf');
$sql = "SELECT * FROM gain ORDER BY hotel, date";
$resu...

$mysqli = new mysqli('127.0.0.1', 'your_user', 'your_pass', 'wf');
$sql = "SELECT * FROM gain ORDER BY hotel, date";
$resu...

Window Function
One of the biggest “news” of MySQL 8
Meetup PUG
30 Aprile 2019
#AperiTech

Index
● Window function history
● What it is
● Types of window function
● Logical ﬂow
● Optimization

Who am I?
I’m Davide Dell’Erba
Full Stack Web Developer @
@delda80
github.com/delda
info@davidedellerba.it

Window function story
Window and window function were ﬁrst introduced to
SQL:1999 as amendment.
Window functions were inco...

Window function story
Along the years, almost all major database systems introduced this feature:
2008 2009 2010 2011 2012...

What is a “window”?
It is a set of rows deﬁned by OVER() clause
Set one
Set two
Set three
ORDER BY()
Set one
Set two
Set t...

What is a “function”?
Function Example
Ranking ROW_NUMBER(), RANK(), DENSE_RANK(), NTILE()
Aggregate MIN(), MAX(), AVG(), ...

So… What is a “window function”?
● It is a function that computes a value for a row using a window
● Operates on a window,...

GROUP BY() vs OVER()
SELECT
key,
SUM(values)
FROM table
GROUP BY key;
SELECT
key,
SUM(value) OVER (PARTITION BY key
ORDER ...

Getting OVER()
mysql> SELECT hotel, date, sale, SUM(sale) OVER() AS total FROM gain;
+-----------+------------+------+----...

Partition clause
mysql> SELECT hotel, date, sale, SUM(sale) OVER ( PARTITION BY hotel) AS total
FROM gain ORDER BY hotel, ...

Types of window function: partition clause
partition clause
● speciﬁed PARTITION BY clause
● windows are separated by part...

Order by clause
mysql> SELECT hotel, date, sale, SUM(sale) OVER (PARTITION BY hotel ORDER BY
date) AS partial, SUM(sale) O...

Types of window function: order by clause
order by clause
● speciﬁed by ORDER BY clause
● deﬁnes ordering on set
● is supp...

Queries...
mysql> SELECT hotel, date, sale, ROUND(AVG(sale) OVER (PARTITION BY hotel
ORDER BY date), 2) AS average , SUM(s...

Queries...
mysql> SELECT hotel, date, sale, ROUND(AVG(sale) OVER (PARTITION BY hotel
ORDER BY date), 2) AS average, ROUND(...

Update table
mysql> UPDATE gain SET sale = 400 WHERE hotel = 'Manfredi';
mysql> UPDATE gain SET sale = 450 WHERE date = '2...

Frame clause introduction
mysql> SELECT hotel, date, sale, COUNT(sale) OVER ( ORDER BY sale DESC ROWS
BETWEEN UNBOUNDED PR...

Frame clause
mysql> SELECT hotel, sale,
COUNT(sale) OVER (ORDER BY sale ROWS BETWEEN UNBOUNDED PRECEDING AND
CURRENT ROW) ...

Frame clause
mysql> SELECT hotel, sale, COUNT(sale) OVER (ORDER BY sale ROWS BETWEEN
UNBOUNDED PRECEDING AND CURRENT ROW) ...

Frame clause
frame clause
● speciﬁed respect the current row
● allow to tell how far the set is applied
● relationships be...

Order please
Order Clause Function
1 FROM (including JOINs) Choose and join tables
2 WHERE Filters the base data
3 GROUP B...

Order please
mysql> SELECT hotel, date, sale,
RANK() OVER (ORDER BY hotel, date) AS 'rank' FROM gain;
+-----------+-------...

Order please
mysql> SELECT hotel, date, sale,
RANK() OVER (ORDER BY hotel, date) AS 'rank' FROM gain ORDER BY date;
+-----...

Implicit and explicit window function
● Window can be implicit and unnamed:
SELECT SUM(sale) OVER (PARTITION BY sale)
FROM...

Implicit and explicit window function
● A window can inherit from another window adding details
SELECT hotel, date, sale,
...

EXPLAIN WITH JSON
Using the simple EXPLAIN command, you can’t see the window function’s
performance;
alternatively, if you...

EXPLAIN
mysql> EXPLAIN SELECT hotel, date, sale, SUM(sale) OVER() total FROM
gainG
*************************** 1. row ****...

EXPLAIN FORMAT=JSON
EXPLAIN FORMAT=JSON SELECT hotel, date, sale, SUM(sale) OVER() total
FROM gain;
…
"windows": [
{
"name...

Q & A

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