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SQL Exercises news letters, latest issue

#659 (2017-05-20)

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 and replacement:
306 -> 139 (learn stage).
306 - new candidate for being at learning stage from no_more is exposed for discussion (1 point).
Mobile application from Dmitry Ponomarenko is now available for work with site forums. Try this.

The most popular topics of the forum
Topic        Messages
Authors of the week in the forum
Author	Messages
NittyMonkey	42
selber  	5
kassbar		4
pegoopik  	3
Лщыы  	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
Applicants for Top 100 have advanced in rating:
126. Johnnymnemonic (149, 305.764)
129. SN 209 (139, 2247.388)
133. Kursist (130, 107.440)
142. MikhailFG (124, 70.404)
259. Tsarapkin (97, 148.724)
Have been certified last week:
Stas911 (A17224120) [BK] - Volgodonsk, Rossiya
Number of subscribers - 3241
Number of rating's participants - 11758
Number of second-stage's participants - 2997
Number of third-stage's participants - 119
On the learning stage - 215309
Certified specialists in total - 768

ТОР 20

NoPersonNumber of
Last_SelNumber of
1Kreslavskij O.M. (Arcan)1256306306253754260.397203.7052252017-05-132017-05-19
2Dubinskij A.V. (_velial)12552203062427102793.3903368.3692252017-04-152017-05-17
3Krasovskij E.A. (pegoopik)1256306306242502209.08912.6672242017-05-142017-05-19
4Bezhaev A.Yu. (Baser)1253305296192441197.797175.1682222017-01-062017-02-01
5Boiko D. (Angellore)12523052961535124677.3333268.2362182017-03-232017-05-03
6Karasyova N.V. (vlksm)1251221306134008275.181226.9262142017-05-042017-05-14
7Filippkin D.V. (_dimon_)1245115295982737194.624127.9092022016-07-202016-09-29
8Kurochkin P.A. (qwrqwr)1245306305942741250.561159.3151952017-05-132017-05-19
9Movlyanov A.P. (Oct)7245102958913072353.7512448.8471932017-01-232017-04-03
10Kostomarov A.V. (al29)92282113055918361753.6401321.0031862017-05-052017-05-19
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)921410284942229985.9871059.9751242017-05-172017-05-17
14Kuznetsov V.S. (herrRo)1172260234191167478.51173.3351222012-02-082013-06-18
15Grinkevich D.L. (Dmitrij Grinkevich)1320445274671652367.281932.3431092016-04-192017-04-05
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)12061030479328050.38047.237962017-04-172017-05-02
20Tarasov D.B. (Gavrila)916515233942427151.34399.710952012-04-232012-05-25

Best results for last week

1>Rakhmatullin (Ranil)13492702777719 May 2017
2Kartashov 5.5. (mimi789456)161619928326219 May 2017
3Escal Y. (NotASocialist)9451901995218 May 2017
4Komin (Komin)93718018111018 May 2017
5>Mityurin V. (mitvol)88417375435619 May 2017
6Dudochkin A. (dandr)53713013165118 May 2017
7Indeev A.V. (indeev)102013013177519 May 2017
8>Kozlova M. (Auriga_dorado)47410102038019 May 2017
9Kashevarov A.V. (A.Kashevarov)5701001048718 May 2017
10>Boyarskij D. (hardison)72210010162319 May 2017
11Grishunin M.F. (MikhailFG)412490914219 May 2017
12Yakovlenko V.G. (musthacrackezh)733909128818 May 2017
13Poltoranin S.S. (Stas911)463831165418 May 2017
14Chernov D. (Kursist)313080813319 May 2017
15Isavnina (swordy2014)444808130719 May 2017
16>Savin A.Yu. (mirovingin)715707216819 May 2017
17Chukanov V.S. (VSC)417606196819 May 2017
18>Medovik O.G. (chelovek-tort)45606558219 May 2017
19Potapova (Anastasiia174)55505612818 May 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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