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SQL Exercises news letters, latest issue

#672 (2017-08-19)

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.

§
Has corrected a bug with checking the exercises:
50 (SELECT, learn) - new hint.
119 (SELECT, rating) - data from Auriga_dorado.
28 (DML) - formulation from author.
§
The most popular topics of the forum
Topic        Messages
§
Authors of the week in the forum
Author	Messages
pegoopik  	15
selber  	10
A-l-l-a-n	7
Gosha		7
Kursist		7
§
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 (181)
12. smog (155, 200)
82. Kursist (145)
§
Have completed the 2nd-stage testing:
124. MikhailFG (tasks 138, time 108.730)

§
New persons in TOP 100 or have returned (solved exercises and 2nd-stage time):
82. Kursist (154, 180.162)
§
Applicants for Top 100 have advanced in rating:
124. MikhailFG (138, 108.730)
131. y4nzi (139, 16.505)
137. Gosha (133, 352.131)
148. Auriga_dorado (120, 41.864)
186. SPMV (116, 970.280)
205. uon (110, 2653.333)
§
Statistics:
Number of subscribers - 2993
Number of rating's participants - 11887
Number of second-stage's participants - 3017
Number of third-stage's participants - 122
On the learning stage - 223839
Certified specialists in total - 777

ТОР 20

NoPersonNumber of
Sel_ex
Last_SelNumber of
DML_ex
ScoresDaysDays_2Days_3S_3LastSolvedLastVisit
1Krasovskij E.A. (pegoopik)1259181316332595209.86413.7522302017-08-152017-08-18
2Bezhaev A.Yu. (Baser)1258225316302636199.973177.3102272017-07-202017-08-16
3Kreslavskij O.M. (Arcan)1257306316283818261.321203.7052252017-07-162017-08-17
4Dubinskij A.V. (_velial)12552203062427102793.3903368.3692252017-04-152017-08-08
5Boiko D. (Angellore)12523052961535124677.3333268.2362182017-03-232017-05-03
6Karasyova N.V. (vlksm)1251221306134008275.181226.9262142017-05-042017-08-14
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)1245306315952804250.323159.3151952017-07-152017-08-18
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)92212002951223211017.3531084.6651372017-08-172017-08-18
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)1320510274682059367.305932.3431092017-05-312017-07-21
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)12061031480338150.38047.237962017-07-272017-07-21
20Tarasov D.B. (Gavrila)916515233942427151.34399.710952012-04-232012-05-25

Best results for last week

Nosurnamen_selsel_allsel_scoresdml_scoresscoresratinglast_visit
1>Belov (mbelov1567)164230030103918 Aug 2017
2>L'vova M. (mlvova)1724212748162618 Aug 2017
3Smirnov A.S. (vvorkandrey)10502002088718 Aug 2017
4Dodonov V.E. (Vladislav Dodonov)84019019105416 Aug 2017
5>Aliev R. (y4nzi)71391801813118 Aug 2017
6Vasilevskaya E.A. (kattiks)8501601688618 Aug 2017
7Vinogradova S.M. (Tigra1)5791001036618 Aug 2017
8>Kozlova M. (Auriga_dorado)212090914818 Aug 2017
9Plugin V. (Basilik)45180880818 Aug 2017
10Maria (Gnommi Mari)3666101649716 Aug 2017
11Kukushkin S.A. (smog)22216061218 Aug 2017
12Leschyov S.V. (SPMV)311660618613 Aug 2017
13chernyaev R.Yu. (Svenfischer1988)412606243718 Aug 2017
14>ganisetti A. (ganisetti)56606546518 Aug 2017
15>Grishunin M.F. (MikhailFG)113850512418 Aug 2017
16Polyakov A.I. (Alexander Green)25850574915 Aug 2017
17Krasovskij E.A. (pegoopik)1259404118 Aug 2017
18Grishaev P.B. (Pavel Borisovich)38404514114 Aug 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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