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How do you start studying SQL?

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guilherme last edited by

Dear friends!
Please advise on how best to start studying the software environment of the SQL bases if there is experience in looting.=) Thank you very much.
With respect DataRs.
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jeanid last edited by

http://www.sql-tutorial.ru/ You can read, http://www.sql-ex.ru/ You can decide. For starters, it's a good one;
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ORA-06502: PL/SQL: the exactness of the number is too large a error of number or value
Software Programming • sql oracle • • terrea

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Here's the thing. You have a procedure. pPair2TwoStr variables p_LEFT and p_RIGHT Unsuccessful receives restriction, allowed varchar2(15)and when the procedure is called, the variable values p_LEFT and p_RIGHT Trying to sign up. sCode U_SUBSCR_CTL.CODE%type and iYear U_SUBSCR_CTL.YEAR%type where restrictions are less than in the procedure.Example:CREATE OR REPLACE PROCEDURE PTEST(I_PAR IN OUT NUMBER, II_PAR IN OUT VARCHAR2) IS BEGIN I_PAR := 15.6; II_PAR := 'POIUYTREWQLKJHGFDSA'; END PTEST; We get something like:CREATE OR REPLACE PROCEDURE PTEST(I_PAR IN OUT NUMBER(3.4), II_PAR IN OUT VARCHAR2(19)) Now, if you make this call:DECLARE V_STR VARCHAR2(10); V_NUM NUMBER(3,4); BEGIN PTEST(V_NUM, V_STR); END; And the mistake is:DECLARE * ошибка в строке 1: ORA-06502: PL/SQL: : буфер символьных строк слишком маленький ошибка числа или значения ORA-06512: на "MILLER.PTEST", line 7 ORA-06512: на line 8 It's not clear what's going on right now, is it? It's very simple, V_STR VARCHAR2(10) Changed the variable restriction II_PAR With its clear challenge and the recording of a long 19 symbol line into a variable of only 10 symbols, it was wrong! It's important to understand that. To avoid this, you can do this:CREATE OR REPLACE PROCEDURE PTEST( I_PAR IN OUT CUSTOMERS.CUST_NUM%TYPE, II_PAR IN OUT CUSTOMERS.COMPANY%TYPE) IS BEGIN I_PAR := 15.6; II_PAR := 'POIUYTREWQLKJHGFDSA'; END PTEST; This is easy by the fact that, when the tables are changed, the machine changes the parameters of the procedures, which facilitates the escort of the code of stored procedures, it is not necessary to change all the parameters of the field involved!
Could not extract ResultSet
Software Programming • sql spring hibernate spring data • • morde

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You have the name of the table matching the reserved name of the "group" function.create table group( id int(2) not null primary key auto_increment, name varchar(255) ) engine = InnoDB;
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Put OBD data into model facilities
Software Programming • java sql • • amarantha

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Elementary. Remember what classes are in java and how they are createdpublic class Pupil { private String name; ... public Pupil(String name, String surname, ...) { this.name = name; ... } public String getName() { return name; } public void setName(String name) { this.name = name; } ... } while (resultSet.next()) { Pupil pupil = new Pupil( resultSet.getObject(1).toString(), resultSet.getObject(2).toString(), ... ); // можно установить свойства с помощью сетера pupil.setClassName(resultSet.getObject(6).toString()); System.out.printf("name %s surname %s ...", pupil.getName(), pupil.getSurname(), ...); }
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SQL: Where in together with Not Where In
Software Programming • mysql sql data base • • zymir

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Second WHERE extra:SELECT * FROM table WHERE column2 IN (2) AND column2 NOT IN (3); In such an approach, the sample should There's only one line. 2 --- 10With this approach, there will be one line: 1 --- 2Possible option:SELECT * FROM table WHERE column2 IN (2) AND column1 NOT IN (SELECT DISTINCT column1 FROM table WHERE column2 IN (3));
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Problems with NOLOCK, READ COMMITTED SNAPSHOT
Software Programming • sql server sql • • rielyn

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The versions of Microsoft SQL Server prior to 2005 did not have the feature SNAPSHOT, then the hint With NOLOCK could in fact improve performance by making a query (a SELECT) not expecting the release of records blocked by a long transaction.Then a brief explanation of each of the terms quoted in your question:COMMITTEEA SELECT run in a session configured as READ COMMITTED will only bring logs already committed. So if this SELECT finds a registry changed by another transaction, it will be waiting for the record to be released by a COMMIT or a ROLBACK.With NOLOCKA SELECT using this hint will also bring records changed by another pending transaction (a transaction that has not yet been completed with COMMIT or ROLBACK). Thus, this SELECT can bring "dirty" records, since you can read a value changed by that transaction but then be restored to its original value in case of a ROLBACK.SNAPSHOTIt is a common resource of database servers that was only introduced in MS SQL Server in your 2005 version.With this active feature, the SGBD keeps a photo of the original status of the registry when it is changed by a transaction. Thus a SELECT in another transaction can read the last commit version of the registry without waiting for the completion of the other pending transaction and without reading a "dirty" record.READ COMMITTED SNAPSHOTA SELECT executed in a section configured with READ COMMITTED SNAPSHOT will read only already committed records, but thanks to the SNAPSHOT feature this SELECT will not be blocked when the registry has been changed by another pending transaction; instead, SELECT will read the latest commit version of the registry.Your questions:1 - NOLOCK even improves performance or is myth, do I have a way to measure this through a consultation with SET STATISTICS TIME ON for example?It can improve yes because your SELECTs will never get blocked. Improves performance significantly in systems (bad) that use many long transactions. This is very difficult to measure as a blocked SELECT will take more or less depending on the simultaneous use of the system by other users.2 - How do I use READ COMMITTED SNAPSHOT? some practical example that can be measured too?You must enable this feature SNAPSHOT in the database (in version 2005 it was deactivated by default - I don't know if it changed in the following versions) and you should set up your sessions to use this level of transaction isolation (read commit snapshot). With this you can stop using the hint WITH NOLOCK without suffering from blocked SELECTs. It's probably the right thing to do. Unfortunately this is also difficult to measure for the same reason already mentioned: performance gain depends on the simultaneous use of the system by other users.3 - What are the correspondents in MySQL and ORACLE?I do not know an equivalent to the hint WITH NOLOCK in these SGBDs, but the fact is that they have the feature SNAPSHOT and it comes activated by default.I tried to be succinct in a rather complex subject. If something was not clear leave a comment that I will improve the answer.
How to concatenate two fields and use as a key to query in the SAS sql process, as well as is done in the excerpt of the example sql?
Software Programming • square • • Marcee

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You will need to use the CONCAT() function.Ex: CONCAT(cod_operadora, ' | ', num_contrato)
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Microsoft sql server management studio entrance error
Software Programming • sql server sql • • guilherme

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You probably don't have SQL. Open the list of services. Windows are listed in the window. Find something like SQL Server or MS SQL Server and choose in the context menu "Put it." After the launch, it's gonna make money.
How can I form a request to MSSQL for a conclusion from several tables?
Software Programming • sql server sql • • morde

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We can dynamite the request and then execute it by the operator.declare @query VARCHAR(max) select @query = coalesce(@query + ' UNION ALL ', '') + 'select * from ' + name from sys.tables where name like 'very_strong_table_%' and schema_id = SCHEMA_ID('dbo') execute (@query)
Help me dissolve XML in T-SQL
Software Programming • sql server sql • • carriann

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You identified the symbol @ The one that's used to access the attributes, and you just need a tag.select @x.value('(/Response/Requests)[1]', 'nvarchar(max)')
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SQL stringnation
Software Programming • mysql sql string varc languagehar c languageontaining strin • • zymir

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You are looking for capabilities http://dev.mysql.com/doc/refman/5.7/en/fulltext-search.html (from MySQL 5.6.4 http://dev.mysql.com/doc/refman/5.6/en/innodb-table-and-index.html#innodb-fulltext-index ).ALTER TABLE sv_users ADD FULLTEXT INDEX (userNome, userSobrenome); And for consultation:SELECT * FROM sv_users WHERE MATCH (userNome, userSobrenome) AGAINST ('Luitame de Oliveira' IN BOOLEAN MODE) If MySQL facilities are not enough (usually not) you can use an external tool like http://lucene.apache.org/solr/ , http://sphinxsearch.com/ or http://www.elasticsearch.org/ . These tools have facilities that leave http://dev.mysql.com/doc/refman/5.7/en/fulltext-boolean.html and in http://dev.mysql.com/doc/refman/5.7/en/fulltext-natural-language.html MySQL in the slipper, can treat abbreviations, synonyms, spelling errors, similar words, etc. In addition, they are much more robust when the number of queries grows. UPDATE: Examples demonstrating my point about the MySQL version and Full Text Search support in InnoDB.Demo I: http://sqlfiddle.com/#!2/0b0f0/19 Demo II: http://sqlfiddle.com/#!9/fee97/4 I didn't want to enter that level of talhe in the answer, but as @Kenny did a query without using the http://dev.mysql.com/doc/refman/5.7/en/fulltext-boolean.html it is important to note that even without special operators, this option makes a difference if you use engine MyISAM (and I kept my habits of that time). With Boolean Mode spaces act as the operator OU (and you can build similar Google queries with +, -, etc.). In the case of InnoDB the two queries return the same result if you do not use a special operator, but it is still interesting to be used to avoid the https://stackoverflow.com/questions/3283706/how-to-disable-mysqls-match-querys-50-exclusion (it should not be relevant in your case unless more than 50% of your users are called Maria or João, but it is good to know if you index some very popular word).
SQL / Correlated request
Software Programming • sql server sql • • Analeea

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Correlated is called a sub-acquisition using the data field values of an external request. For exampleSELECT ContactName FROM Customers WHERE EXISTS ( SELECT NULL FROM Orders WHERE Customers.CustomerID = Orders.CustomerID AND Orders.ShipperID = 3);
Starting is slow.
Software Programming • video command line ffmpeg • • Bogopo

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The thing is, -ss It's in the commanded team after the input.To make it quick, you have to put this parameter in front of everyone. -i:ffmpeg -ss 42:47 -i "smth.flv" -t 49 -vcodec h264 -acodec copy -format avi "smth.avi" Source: https://stackoverflow.com/a/42639384/4928642
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Simulation of column values in request
Software Programming • mysql sql • • simrah

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SELECT `class`, `discipline`, SUM(IF(`type`='Лабораторная', `count_students`, 0)) AS `count_students`, SUM(IF(`type`='Лекция', `count_hours`, 0)) AS `lection`, SUM(IF(`type`='Семинар', `count_hours`, 0)) AS `seminar`, SUM(IF(`type`='Лабораторная', `count_hours`, 0)) AS `lab`, SUM(`type`='Лекция') AS `groups`, SUM(`type`='Лабораторная') AS `subgroups`, count('id') AS `numbe`, `course_semestr`, `profile`, `id`, (SUM(IF(`type`='Лекция', `count_hours`, 0)) -- + SUM(IF(`type`='Семинар', `count_hours`, 0)) -- + SUM(IF(`type`='Лабораторная', `count_hours`, 0))) as total_hours -- исправление здесь FROM `list` GROUP BY `class`, `discipline`; or so:SELECT * , (`lection` + `seminar` + `lab`) as total_hours FROM (SELECT `class`, `discipline`, SUM(IF(`type`='Лабораторная', `count_students`, 0)) AS `count_students`, SUM(IF(`type`='Лекция', `count_hours`, 0)) AS `lection`, SUM(IF(`type`='Семинар', `count_hours`, 0)) AS `seminar`, SUM(IF(`type`='Лабораторная', `count_hours`, 0)) AS `lab`, SUM(`type`='Лекция') AS `groups`, SUM(`type`='Лабораторная') AS `subgroups`, count('id') AS `numbe`, `course_semestr`, `profile`, `id` FROM `list` GROUP BY `class`, `discipline`); And the report generators are all looking for information.P.S. Sorry, he misunderstood the question, and accordingly gave the wrong answer, the decision gives the sum of three columns, not the total for each, the right answer for @Alex to use ROLLUP
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How to start Timer. Start a service by clicking a button?
Software Programming • winforms vb.net windows servic languagee • • emerson

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If both applications are on the same machine, you can manipulate them through files.You make your button create a file inside a folder, which as soon as your other application finds it, it performs the action you want.For example:In your windows service project, create a timer with a short range only by checking the existence of the file.System.Timers.Timer _timer = new System.Timers.Timer { Interval = 30000, Enabled = true, AutoReset = true }; _timer.Elapsed += Init; _timer.Start(); void Init(object source, ElapsedEventArgs e) { var file = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData), "my_app_folder", "start_file"); if (File.Exists(file)) { File.Delete(file); //Deleta para não executar novamente na proxima vez que o timer executar //IniciaProcesso } } It would also be interesting if a kind of token was generated and recorded inside the file to ensure that the generated file was actually your system.
Oracle SQL
Software Programming • sql oracle • • briley

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You've got a mistake in baseline data. To be in the last line BFYou need to fix this. parent_id in the last line 5 ♪ 2♪ Here we go.with t as ( select 1 host_id, null parent_id, 'A' name from dual union all select 2 host_id, null parent_id, 'B' name from dual union all select 3 host_id, null parent_id, 'C' name from dual union all select 4 host_id, 1 parent_id, 'D' name from dual union all select 5 host_id, 4 parent_id, 'E' name from dual union all select 6 host_id, 2 parent_id, 'F' name from dual) select host_id, replace(sys_connect_by_path(name, ' '), ' ', '') name from t connect by prior host_id = parent_id start with parent_id is null order by host_id UPD.Back to the chase.You can use the so-called "precurate" WITH"He gives a little control over the process:with t as ( select 1 host_id, null parent_id, rpad('A', 2000, ' ') name from dual union all select 2 host_id, null parent_id, rpad('B', 2000, ' ') name from dual union all select 3 host_id, null parent_id, rpad('C', 2000, ' ') name from dual union all select 4 host_id, 1 parent_id, rpad('D', 2000, ' ') name from dual union all select 5 host_id, 4 parent_id, rpad('E', 2000, ' ') name from dual union all select 6 host_id, 2 parent_id, rpad('F', 2000, ' ') name from dual), rec (host_id, name) as (select host_id, name from t where parent_id is null union all select t.host_id, case when length(t.name) + length(rec.name) <= 4000 then rec.name else rec.name || t.name end name from t join rec on rec.host_id = t.parent_id and length(t.name) + length(rec.name) <= 4000 ) select * from rec Operator seat. CASE It is not possible to add symbols if the result is longer than 4,000, but a condition and length(t.name) + length(rec.name) <= 4000 It's possible to cut off those lines. Use something better, of course.

How do you start studying SQL?

Suggested Topics

ORA-06502: PL/SQL: the exactness of the number is too large a error of number or value Software Programming • sql oracle • • terrea

Could not extract ResultSet Software Programming • sql spring hibernate spring data • • morde

Put OBD data into model facilities Software Programming • java sql • • amarantha

SQL: Where in together with Not Where In Software Programming • mysql sql data base • • zymir

Problems with NOLOCK, READ COMMITTED SNAPSHOT Software Programming • sql server sql • • rielyn

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Starting is slow. Software Programming • video command line ffmpeg • • Bogopo

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How to start Timer. Start a service by clicking a button? Software Programming • winforms vb.net windows servic languagee • • emerson

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ORA-06502: PL/SQL: the exactness of the number is too large a error of number or value
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Could not extract ResultSet
Software Programming • sql spring hibernate spring data • • morde

Put OBD data into model facilities
Software Programming • java sql • • amarantha

SQL: Where in together with Not Where In
Software Programming • mysql sql data base • • zymir

Problems with NOLOCK, READ COMMITTED SNAPSHOT
Software Programming • sql server sql • • rielyn

How to concatenate two fields and use as a key to query in the SAS sql process, as well as is done in the excerpt of the example sql?
Software Programming • square • • Marcee

Microsoft sql server management studio entrance error
Software Programming • sql server sql • • guilherme

How can I form a request to MSSQL for a conclusion from several tables?
Software Programming • sql server sql • • morde

Help me dissolve XML in T-SQL
Software Programming • sql server sql • • carriann

SQL stringnation
Software Programming • mysql sql string varc languagehar c languageontaining strin • • zymir

SQL / Correlated request
Software Programming • sql server sql • • Analeea

Starting is slow.
Software Programming • video command line ffmpeg • • Bogopo

Simulation of column values in request
Software Programming • mysql sql • • simrah

How to start Timer. Start a service by clicking a button?
Software Programming • winforms vb.net windows servic languagee • • emerson

Oracle SQL
Software Programming • sql oracle • • briley