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SQL Exercises news letters, latest issue

#677 (2017-09-23)

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 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
Sulviya		11
pegoopik  	6
qwrqwr  	5
Kursist		4
rait		4
§
Available competitions on query optimization
Exercise	Date	     Author
147	2012-02-23	$erges
159	2012-07-25	anddros
170	2011-07-15	qwrqwr
182	2012-02-16	Baser
192	2012-03-03	Baser
197	2014-11-06	pegoopik
214	2015-06-24	pegoopik
259	2012-07-23	anddros
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Additional non-optimization competitions
Exercise	Date	Author/Organizer of competition
71	2010-12-26	anddros (closed)
88	2012-07-12	crescent/Pegoopik  (closed)
91	2012-05-31	smog/$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):
12. smog (161)
40. y4nzi (140, 144, 150, 158, 177)
61. Kursist (173, 225)
65. selber (141)
§
Applicants for Top 100 have advanced in rating:
126. Gosha (146, 486.785)
179. shipwright (109, 185.295)
267. Tigra1 (96, 14.058)
293. GiBis (89, 13.995)
§
Statistics:
Number of subscribers - 2999
Number of rating's participants - 11911
Number of second-stage's participants - 3026
Number of third-stage's participants - 124
On the learning stage - 227402
Certified specialists in total - 781

ТОР 20

NoPersonNumber of
Sel_ex
Last_SelNumber of
DML_ex
ScoresDaysDays_2Days_3S_3LastSolvedLastVisit
1Krasovskij E.A. (pegoopik)1259181316332595209.86413.7522302017-08-152017-09-22
2Bezhaev A.Yu. (Baser)1258225316302636199.973177.3102272017-07-202017-09-22
3Kreslavskij O.M. (Arcan)1258225316303867265.524207.9082272017-09-032017-09-22
4Dubinskij A.V. (_velial)12552203062427102793.3903368.3692252017-04-152017-09-06
5Boiko D. (Angellore)12523052961535124677.3333268.2362182017-03-232017-05-03
6Karasyova N.V. (vlksm)1251221306134008275.181226.9262142017-05-042017-09-20
7Kostomarov A.V. (al29)72352233057819191835.7821403.1442052017-07-272017-08-04
8Filippkin D.V. (_dimon_)1245115295982737194.624127.9092022016-07-202016-09-29
9Kurochkin P.A. (qwrqwr)1246305315962863250.449159.3151952017-09-122017-09-22
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)92251612952523551046.6601113.9711502017-09-202017-09-22
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
18Vyazovetskov A.S. (alex_v)15177187234063246123.34242.620972015-04-282015-06-05
19Timofeeva E.V. (Umrikhina)12061031480338150.38047.237962017-07-272017-08-31
20Tarasov D.B. (Gavrila)916515233942427151.34399.710952012-04-232012-05-25

Best results for last week

Nosurnamen_selsel_allsel_scoresdml_scoresscoresratinglast_visit
1>Osin (anyman1979)233332133215222 Sep 2017
2>Zhulanov S.G. (borey.mdb)94321021102522 Sep 2017
3>Savin A.Yu. (mirovingin)8481601693022 Sep 2017
4Aliev R. (y4nzi)5169140144022 Sep 2017
5>Shalavin D.E. (Juster81)83713013120422 Sep 2017
6Semin R.Yu. (Roman7in)82313013184820 Sep 2017
7bokr (qwerty)75111011100521 Sep 2017
8>anderson C.7. (andersoncouncil)9911011485522 Sep 2017
9Polikarpova E. (Filisity)8810010513720 Sep 2017
10>Vinogradova S.M. (Tigra1)49690926722 Sep 2017
11Baklanov V.K. (Vorfian)429808123322 Sep 2017
12Kroshin (storm74)88808543220 Sep 2017
13Polyakov A.I. (Alexander Green)36170769721 Sep 2017
14>Plugin V. (Basilik)35470774122 Sep 2017
15Bezgin (TonyKas)5562733299421 Sep 2017
16>Lotar70 (Lotar70)419606186522 Sep 2017
17Kirdan (shipwright)310951617922 Sep 2017
18Daschinskij I. (ivan dasch)3342731311821 Sep 2017
19Koptel'tsev V. (selber)11764046522 Sep 2017
20Drozdov A.A. (Drozdov Aleksandr)38404532717 Sep 2017
21>Kopyonkin (ringman)33404729622 Sep 2017
22>Mazurov V.A. (Kiot)33404730522 Sep 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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