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January 20, 04:20 MSK


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SQL Exercises news letters, latest issue

#694 (2018-01-20)

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 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
selber  		10
Kursist		7
vasilyvanc  	7
pegoopik  	6
qwrqwr  	6
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 (228)
3. Arcan (228)
6. vlksm (228)
9. qwrqwr (228)
14. alex_v (153, 228)
23. y4nzi (184)
64. selber (228)
114. MikhailFG (140)
Have completed the 2nd-stage testing:
126. Gosha (tasks 156, time 605.947)

Applicants for Top 100 have advanced in rating:
114. MikhailFG (144, 110.588)
126. Gosha (156, 605.947)
190. pavel1211 (114, 42.234)
195. alan1 (111, 314.855)
211. parra (104, 461.421)
236. Lesya1 (107, 247.827)
Number of subscribers - 3015
Number of rating's participants - 11956
Number of second-stage's participants - 3048
Number of third-stage's participants - 126
On the learning stage - 239025
Certified specialists in total - 788

ТОР 20

NoPersonNumber of
Last_SelNumber of
1Krasovskij E.A. (pegoopik)1263228336442749209.94313.8142352018-01-162018-01-19
2Boiko D. (Angellore)12633063364437805232.3843821.1172352017-12-162018-01-09
3Kreslavskij O.M. (Arcan)1263228336433999269.462210.7962342018-01-132018-01-19
4Bezhaev A.Yu. (Baser)1258225316302636199.875177.3102272017-07-202017-12-12
5Dubinskij A.V. (_velial)1258693363229842793.5243368.3692252018-01-142018-01-17
6Karasyova N.V. (vlksm)1258228336294263288.637239.9832202018-01-142018-01-19
7Kostomarov A.V. (al29)72382123159020912392.7692155.9642162018-01-152018-01-16
8Filippkin D.V. (_dimon_)1245115295982737194.554127.9092022016-07-202016-09-29
9Kurochkin P.A. (qwrqwr)1251228336092985253.034161.5222002018-01-122018-01-19
10Movlyanov A.P. (Oct)7245102958913072353.7232448.8471932017-01-232017-04-03
11Sal'nikov S.A. ($erges)122820625552253317.50514.4981812015-02-022017-04-13
12Kukushkin S.A. (smog)92261632952823681054.5621122.1811532017-10-032018-01-18
13Yatsuk A.A. (Faust_zp)1187255244601984144.150108.8401372012-07-122012-07-30
14Vyazovetskov A.S. (alex_v)14212153234854242137.14953.9551282018-01-182018-01-19
15Kuznetsov V.S. (herrRo)1172260234191167478.51173.3351222012-02-082013-06-18
16Doschenko V.N. (mcrain)152012193348122781817.100302.2771122017-12-272018-01-19
17Grinkevich D.L. (Dmitrij Grinkevich)1320510274682059367.128932.3431092017-05-312018-01-11
18Drozdkov A.N. (anddros)51931624446224412.34111.0911082014-07-212015-01-29
19Shindin A.V. (AlShin)114825223367928408.505777.457992011-05-052014-05-18
20Timofeeva E.V. (Umrikhina)12061031480338150.34747.237962017-07-272018-01-19

Best results for last week

1Malyshkin (Andrey_Mal)142922022246618 Jan 2018
2>Mendoza A. (AlvaroMendoza)113719019174619 Jan 2018
3Zvon (pavel1211)71141401419019 Jan 2018
4Pusev D.V. (Pusev_Denis)47290971219 Jan 2018
5Volkov S. (ctacukoc)623808166319 Jan 2018
6Radin P.L. (RadinPL)520808178119 Jan 2018
7>G N.E. (gana)716808412419 Jan 2018
8>Viktorov V. (viktor-orenb)55707572519 Jan 2018
9>Karpeshin E.N. (Zealdequar)28060637019 Jan 2018
10Sonic S.S. (Sonic_ru)536606152916 Jan 2018
11Lavrov K. (Senarist1)55606590618 Jan 2018
12Vyazovetskov A.S. (alex_v)22125051419 Jan 2018
13Shkarednyj (Gosha)115650512619 Jan 2018
14Savin A.Yu. (mirovingin)36650562119 Jan 2018
15>KsNV (KsNV_)239505114419 Jan 2018
16Shabanov R.R. (Vertel)237505116819 Jan 2018
17Grishunin M.F. (MikhailFG)214440411418 Jan 2018
18Nikanorov (parra)110440421119 Jan 2018
19Il'nitskij S.N. (flipper)28040439717 Jan 2018

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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