SQL exercises
Language 
March 25, 03:01 MSK
Login:

Password:

forgot password?
Registration

Transact-SQL tests
Personal page
Developers & Thanks
For employers
References
Feedback
Support SQL-EX.RU



Poll
Would you get the following certificate?
Yes 68.5%
No 12.1%
Probably I would get it for supporting the project 9.4%
Such certificate is unnecessary one 5.6%
Such certificate is necessary on a site, but not for me 4.5%



Total Votes: 36561
 


Купите качественную кухню эконом класса от производителя
siriusmebelspb.ru

merten-sale
MERTEN все серии в наличие!Доставка по РФ! Спецпредложения дизайнерам
merten-sale.ru

оцилиндрованное бревно
brevius.ru

SQL Exercises news letters, latest issue

#651 (2017-03-25)

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
_velial  	10
pegoopik  	9
ksiarhei	6
NotASocialist	5
Kursist		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):
3. _velial (218, 219, 221, 222, 223)
§
Applicants for Top 100 have advanced in rating:
132. Johnnymnemonic (143, 276.814)
185. Kursist (108, 66.119)
213. gipsy (108, 3731.747)
219. MikhailFG (100, 41.858)
228. Lesya1 (104, 169.843)
§
Statistics:
Number of subscribers - 3240
Number of rating's participants - 11681
Number of second-stage's participants - 2975
Number of third-stage's participants - 119
On the learning stage - 210196
Certified specialists in total - 762

ТОР 20

NoPersonNumber of
Sel_ex
Last_SelNumber of
DML_ex
ScoresDaysDays_2Days_3S_3LastSolvedLastVisit
1Krasovskij E.A. (pegoopik)1255306296222438207.80411.7022232017-03-112017-03-24
2Kreslavskij O.M. (Arcan)1255306296213691258.366201.7732222017-03-112017-03-24
3Dubinskij A.V. (_velial)12552222962126862793.2323368.2072222017-03-222017-03-24
4Bezhaev A.Yu. (Baser)1253305296192441197.797175.1682222017-01-062017-02-01
5Boiko D. (Angellore)12533052961635124677.3373268.2362182017-03-232017-03-24
6Karasyova N.V. (vlksm)1251221296123914275.181226.9262142017-01-302017-03-20
7Filippkin D.V. (_dimon_)1245115295982737194.624127.9092022016-07-202016-09-29
8Kurochkin P.A. (qwrqwr)1245306295932677250.319159.3151952017-03-102017-03-24
9Movlyanov A.P. (Oct)72463062959013562353.7572448.8471932017-03-132017-03-24
10Sal'nikov S.A. ($erges)122820625552253317.53314.4981812015-02-022016-08-11
11Kostomarov A.V. (al29)92182512953917851731.3851316.8801812017-03-152017-03-23
12Yatsuk A.A. (Faust_zp)1187255244601984144.150108.8401372012-07-122012-07-30
13Kukushkin S.A. (smog)9213115274922115985.9781059.9751242017-01-232017-02-28
14Kuznetsov V.S. (herrRo)1172260234191167478.51173.3351222012-02-082013-06-18
15Grinkevich D.L. (Dmitrij Grinkevich)1320445274671652367.281932.3431092016-04-192017-02-25
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)12061029478321450.38047.237962017-02-102017-02-27
20Tarasov D.B. (Gavrila)916515233942427151.34399.710952012-04-232012-05-25

Best results for last week

Nosurnamen_selsel_allsel_scoresdml_scoresscoresratinglast_visit
1Shaidullin I.I. (skaterofnk)10432302398423 Mar 2017
2Antonovich M. (Masha279)114120020154424 Mar 2017
3Dubinskij A.V. (_velial)525513013324 Mar 2017
4>Mityurin V. (mitvol)84413013153424 Mar 2017
5Ignatov D. (actsys)99112637262824 Mar 2017
6>Grishunin M.F. (MikhailFG)31001101121924 Mar 2017
7Chmelyov G.A. (Grigory630)83311011195423 Mar 2017
8>Akimova (inkog_ni_to)527909125724 Mar 2017
9>Pantileenko D. (iriswind1)621909169024 Mar 2017
10Votrina A. (Almir4ik)37180842322 Mar 2017
11>Shevchenko (kolbasometr)45880870824 Mar 2017
12Kondratenko E. (Capt_Jack_Sparrow)714707216021 Mar 2017
13Ershov P.S. (pashae)326707285720 Mar 2017
14lee (donlee460)51951116186018 Mar 2017
15>Chernov D. (Kursist)210853818523 Mar 2017
16V (Voltavi)238505104424 Mar 2017
17Kuzovov K.D. (xynshine)44841578419 Mar 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

Useful links

§ All articles from news letters are putting on the site Books and articles about SQL thereafter.

§ We invite you to visit the Interactive SQL textbook.
    The resource is positioned as a "handbook" for this site SQL-EX.COM, but can be used irrespective of it also.

§ The following DBMS are used on the site for solving exercises: SQL Server 2012 Express, Oracle Database 11g Express Edition, MySQL 5, PostgreSQL 9.

§ If you like this site, vote for us:
del.icio.us
dzone.com
Digg.com
stumbleupon.com



Home
Week news
Profile
References
Rambler's Top100
Copyright SQL-EX © 2002-2017. All rights reserved.
contact