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SQL Exercises news letters, latest issue

#646 (2017-02-18)

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.
§
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
selber  	7
eugene.dnepr	7
vlksm  		4
qwrqwr  	3
kay1992		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):
27. Sleeping (200)
62. mcrain (213)
102. selber (256)
§
Applicants for Top 100 have advanced in rating:
102. selber (167, 585.678)
121. VadimI (142, 21.091)
129. wqer (133,84.248)
137. IlyaB (132, 2451.072)
243. Kursist (98, 40.875)
§
Have been certified last week:
nipah~~~ (A17352312) [BK] - g. Moskva, Rossiya
ZG (A17039216) [BK] - g. Moskva, Rossiya
Alexey88 (A17307224) [BK] - g. Krasnogorsk, Rossiya
§
Statistics:
Number of subscribers - 3234
Number of rating's participants - 11723
Number of second-stage's participants - 2963
Number of third-stage's participants - 118
On the learning stage - 206698
Certified specialists in total - 762

ТОР 20

NoPersonNumber of
Sel_ex
Last_SelNumber of
DML_ex
ScoresDaysDays_2Days_3S_3LastSolvedLastVisit
1Kreslavskij O.M. (Arcan)1254222296203652258.362201.7732222017-01-312017-02-17
2Bezhaev A.Yu. (Baser)1253305296192441197.797175.1682222017-01-062017-02-01
3Boiko D. (Angellore)12512222961434354677.3153268.2362182017-01-052017-02-16
4Karasyova N.V. (vlksm)1251221296123914275.181226.9262142017-01-302017-02-14
5Krasovskij E.A. (pegoopik)5250154296092401207.38411.2862112017-02-022017-02-16
6Filippkin D.V. (_dimon_)1245115295982737194.624127.9092022016-07-202016-09-29
7Kurochkin P.A. (qwrqwr)124410295922628250.316159.3151952017-01-202017-02-17
8Movlyanov A.P. (Oct)7245102958913072353.7512448.8471932017-01-232017-02-17
9Dubinskij A.V. (_velial)1241102958626332601.5413176.5401892017-01-282017-02-15
10Sal'nikov S.A. ($erges)122820625552253317.53314.4981812015-02-022016-08-11
11Kostomarov A.V. (al29)92091152951817451698.7651284.6831662017-02-032017-02-17
12Yatsuk A.A. (Faust_zp)1187255244601984144.150108.8401372012-07-122012-07-30
13Kukushkin S.A. (smog)9213115274922115985.9781059.9751242017-01-232017-01-23
14Kuznetsov V.S. (herrRo)1172260234191167478.51173.3351222012-02-082013-06-18
15Grinkevich D.L. (Dmitrij Grinkevich)1320445274671652367.281932.3431092016-04-192017-02-09
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)12061029478321450.38047.237962017-02-102017-02-09
20Tarasov D.B. (Gavrila)916515233942427151.34399.710952012-04-232012-05-25

Best results for last week

Nosurnamen_selsel_allsel_scoresdml_scoresscoresratinglast_visit
1>Efremov N.A. (Nikita86)21634004062117 Feb 2017
2Kazakov I.B. (nipah~~~)107820103039715 Feb 2017
3>Rusakov S.S. (Stas123)151918018181317 Feb 2017
4Grishunin M.F. (MikhailFG)8841732031617 Feb 2017
5>Karlov A. (Skynet17)92914014133817 Feb 2017
6Cherbaev A. (Alexey88)66313284162716 Feb 2017
7Ilyasov V. (VadimI)41421101112116 Feb 2017
8Chukavin M. (rfv45uklwd)61782432210417 Feb 2017
9>Kirdan (shipwright)37380833817 Feb 2017
10country K. (countryKZ)238606107717 Feb 2017
11Bukreev A. (AlxB)237606108916 Feb 2017
12Sil'van (silvr)626606153117 Feb 2017
13Trofimov A.V. (jacksql)419606366517 Feb 2017
14Chernov D. (Kursist)39850524317 Feb 2017
15>P_ N. (no_more)323505310717 Feb 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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