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SQL Exercises news letters, latest issue

#681 (2017-10-21)

Week news

§
As the important news can appear and between releases of news letters, I shall use this page for the publication of the information on all changes on the site.
The forum is not so suitable for this purpose since the message there "escapes" and can appear on previous page before it will lose a urgency.
So look in here if you wish to be well informed about last events on the site. The link to this page is in section of news at the main page below a subscription banner.
§
New exercise (DML) from selber is added under the number of 32 (2 points).


§
New version of mobile application from Dmitry Ponomarenko is now available for work with site forums and more. Try this.

§
The most popular topics of the forum
Topic        Messages
§
Authors of the week in the forum
Author	Messages
vilenia		8
Kursist		3
mcrain  		3
kay1992		3
pegoopik  	3
§
Available competitions on query optimization
Exercise	Date	     Author
147	2012-02-23	$erges
159	2012-07-25	anddros
170	2011-07-15	qwrqwr
182	2012-02-16	Baser
192	2012-03-03	Baser
197	2014-11-06	pegoopik
214	2015-06-24	pegoopik
259	2012-07-23	anddros
§
Additional non-optimization competitions
Exercise	Date	Author/Organizer of competition
71	2010-12-26	anddros (closed)
88	2012-07-12	crescent/Pegoopik  (closed)
91	2012-05-31	smog/$erges
102	2016-07-04	GriGrim/pegoopik
121	2012-07-06	ZrenBy/anddros
153	2010-09-21	Ozzy
§
Changes among leaders (solved exercises of third stage):
1. pegoopik (226)
25. mcrain (194, 226)
34. y4nzi (149)
51. Kursist (201)
§
Applicants for Top 100 have advanced in rating:
124. Gosha (150, 512.303)
207. Tigra1 (107, 18.557)
279. GiBis (92, 15.552)
§
Statistics:
Number of subscribers - 3001
Number of rating's participants - 11922
Number of second-stage's participants - 3032
Number of third-stage's participants - 124
On the learning stage - 230396
Certified specialists in total - 783

ТОР 20

NoPersonNumber of
Sel_ex
Last_SelNumber of
DML_ex
ScoresDaysDays_2Days_3S_3LastSolvedLastVisit
1Krasovskij E.A. (pegoopik)1260226316362655209.86413.7522332017-10-142017-10-20
2Bezhaev A.Yu. (Baser)1258225316302636199.973177.3102272017-07-202017-10-19
3Kreslavskij O.M. (Arcan)1258225316303867265.524207.9082272017-09-032017-10-20
4Dubinskij A.V. (_velial)12552203162528922793.3903368.3692252017-10-142017-10-19
5Boiko D. (Angellore)12523052961535124677.3333268.2362182017-03-232017-05-03
6Karasyova N.V. (vlksm)1253307306164172275.463226.9262142017-10-152017-10-17
7Kostomarov A.V. (al29)72352233057819191835.7821403.1442052017-07-272017-10-17
8Filippkin D.V. (_dimon_)1245115295982737194.624127.9092022016-07-202016-09-29
9Kurochkin P.A. (qwrqwr)1246305315962863250.449159.3151952017-09-122017-10-20
10Movlyanov A.P. (Oct)7245102958913072353.7512448.8471932017-01-232017-04-03
11Sal'nikov S.A. ($erges)122820625552253317.53314.4981812015-02-022017-04-13
12Kukushkin S.A. (smog)92261632952823681054.8691122.1811532017-10-032017-10-13
13Yatsuk A.A. (Faust_zp)1187255244601984144.150108.8401372012-07-122012-07-30
14Kuznetsov V.S. (herrRo)1172260234191167478.51173.3351222012-02-082013-06-18
15Grinkevich D.L. (Dmitrij Grinkevich)1320510274682059367.305932.3431092017-05-312017-09-09
16Drozdkov A.N. (anddros)51931624446224412.34111.0911082014-07-212015-01-29
17Shindin A.V. (AlShin)114825223367928408.505777.457992011-05-052014-05-18
18>Vyazovetskov A.S. (alex_v)1517810234074152123.36542.620972017-10-202017-10-20
19Timofeeva E.V. (Umrikhina)12061031480338150.38047.237962017-07-272017-10-20
20Tarasov D.B. (Gavrila)916515233942427151.34399.710952012-04-232012-05-25

Best results for last week

Nosurnamen_selsel_allsel_scoresdml_scoresscoresratinglast_visit
1>Troitskij (Glam)212628028148220 Oct 2017
2>Shalavin D.E. (Juster81)11812602639920 Oct 2017
3>Igina D.V. (kotopes46)8461601696920 Oct 2017
4>anderson C.7. (andersoncouncil)53813013113720 Oct 2017
5Kopyonkin (ringman)621909175920 Oct 2017
6Nikitenko V.G. (vadim_ni)88909530019 Oct 2017
7>Osin (anyman1979)3738192734220 Oct 2017
8Buldenkov D.A. (eXeQuThor)47680839818 Oct 2017
9Zhulanov S.G. (borey.mdb)37380845618 Oct 2017
10Baranova L. (Luda2)620808355920 Oct 2017
11Doschenko V.N. (mcrain)21897072520 Oct 2017
12>Vinogradova S.M. (Tigra1)310770720720 Oct 2017
13Petrova T. (TPetrova)348707118820 Oct 2017
14>Lukin S. (P1AW)66707567020 Oct 2017
15>Murav'yova L.A. (ladika)428404125020 Oct 2017
16Abramov A.S. (Lion0k)413404231420 Oct 2017
17>Filippov E.E. (ferrous)2232427337320 Oct 2017

Let's learn SQL

MySQL. Usage of query variables

E.A. Krasovskiy

People rather often ask whether there are equivalents for analytic (windowing) functions in MySQL. No, there are not. To replace them, self join queries, complex subqueries, etc, are used. Most of such workarounds turn out to be ineffective.

There are no recursive queries in MySQL either. However, a part of problems usually solved by analytic functions or recursive queries can be handled by features available in MySQL.

One of these features is the unique mechanism of processing variables within a SQL query, which is very unusual for other DBMS. In MySQL, you can declare a variable within a query, change its value, and put it into the result set of the SELECT statement for output. And the most notable thing is, the processing order for query rows, and thus the order values are assigned to variables, can be defined by custom sorting!

Note: this article implies expressions within the SELECT statement are processed in order from left to right; however, there is no confirmation of such a processing order in the official MySQL documentation. You need to keep that in mind when switching from one server version to another. To ensure the required evaluation order, a fake CASE or IF statement can be used.

Read more:
Equivalent of recursive CTEs
Equivalents for analytic functions
Performance

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