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SQL Exercises news letters, latest issue

#668 (2017-07-22)

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
pegoopik  	12
qwrqwr  	7
Baser  		5
Hodges		3
mcrain  	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. Baser (225)
2. Pegoopik (225)
13. smog (147)
31. mcrain (214)
Applicants for Top 100 have advanced in rating:
121. vasilyvanc (157, 88.430)
122. Kursist (148, 145.412)
183. Masha279 (118, 66.310)
187. Auriga_dorado (104, 33.056)
209. SPMV (110, 968.608)
233. y4nzi (103, 7.407)
284. MagicMike (97, 33.860)
Have been certified last week:
mimi789456 (A17296359) [BK] - Moskva, Rossiya
Number of subscribers - 2991
Number of rating's participants - 11851
Number of second-stage's participants - 3006
Number of third-stage's participants - 120
On the learning stage - 220658
Certified specialists in total - 775

ТОР 20

NoPersonNumber of
Last_SelNumber of
1Bezhaev A.Yu. (Baser)1258225316302636199.973177.3102272017-07-202017-07-21
2Krasovskij E.A. (pegoopik)1258306316292564208.77912.6672262017-07-152017-07-21
3Kreslavskij O.M. (Arcan)1257306316283818261.321203.7052252017-07-162017-07-17
4Dubinskij A.V. (_velial)12552203062427102793.3903368.3692252017-04-152017-07-17
5Boiko D. (Angellore)12523052961535124677.3333268.2362182017-03-232017-05-03
6Karasyova N.V. (vlksm)1251221306134008275.181226.9262142017-05-042017-07-21
7Filippkin D.V. (_dimon_)1245115295982737194.624127.9092022016-07-202016-09-29
8Kostomarov A.V. (al29)82332223057218881811.7261379.0881992017-06-262017-07-21
9Kurochkin P.A. (qwrqwr)1245306315952804250.323159.3151952017-07-152017-07-21
10Movlyanov A.P. (Oct)7245102958913072353.7512448.8471932017-01-232017-04-03
11Sal'nikov S.A. ($erges)122820625552253317.53314.4981812015-02-022017-04-13
12Yatsuk A.A. (Faust_zp)1187255244601984144.150108.8401372012-07-122012-07-30
13Kukushkin S.A. (smog)9218306295032292996.3741063.6861282017-07-192017-07-21
14Kuznetsov V.S. (herrRo)1172260234191167478.51173.3351222012-02-082013-06-18
15Grinkevich D.L. (Dmitrij Grinkevich)1320510274682059367.305932.3431092017-05-312017-07-21
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)12061030479328050.38047.237962017-04-172017-07-21
20Tarasov D.B. (Gavrila)916515233942427151.34399.710952012-04-232012-05-25

Best results for last week

1>Aliev R. (y4nzi)211034804823321 Jul 2017
2>Sidorov A.S. (AlexAndNN)12562302383520 Jul 2017
3>Antonovich M. (Masha279)71181201218321 Jul 2017
4Leschyov S.V. (SPMV)51101111220921 Jul 2017
5Trofimov A. (sun_bird)57390945518 Jul 2017
6>Ushakov G.A. (genush)65890968521 Jul 2017
7>Fomin P. (Plinc)542909135021 Jul 2017
8Kovalyov P.A. (Hodges)715707421120 Jul 2017
9>Kozlova M. (Auriga_dorado)310461718721 Jul 2017
10Trofimov A.V. (jacksql)237606166519 Jul 2017
11Kukushkin S.A. (smog)22185051321 Jul 2017
12Doschenko V.N. (mcrain)21845053121 Jul 2017
13>Lysikov M.Yu. (MagicMike)59750528421 Jul 2017
14>Plugin V. (Basilik)341505102021 Jul 2017
15Vasilevskaya E.A. (kattiks)238505110220 Jul 2017
16>Yastrebova (Sib1234)224505151821 Jul 2017
17>Smirnov A.S. (vvorkandrey)411505244521 Jul 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

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