Computers & Technology sql

photoappsios musicappsios strategygamesios

Tutorial Addendum on SQL - Transaction Administration

 MySQL Transaction Abreast Akin Analysis - Apprehend CommittedMy next analysis is about "read committed". Again, I started "session 1" in the first command window: mysqlinmysql testmysql> Baddest Affair 1 ;+-----------+| Affair 1 |+-----------+ mysql> Bead TABLE IF EXISTS User;mysql> Make TABLE User (ID INT PRIMARY KEY, Name CHAR(8)) ENGINE=InnoDB;mysql> Admit INTO User Ethics (2, bill );mysql> Baddest CURRENT_TIME();+----------------+| 21:11:51 |+----------------+mysql> -- abide with affair 2mysql> Amend User SET Name= bob Area ID=2;mysql> Baddest CURRENT_TIME();+----------------+| 21:16:57 |+----------------+mysql> -- abide with affair 2In the additional command window, I acclimated a "read committed" transaction: mysqlinmysql testmysql> Baddest Affair 2 ;+-----------+| Affair 2 |+-----------+ mysql> SET TRANSACTION Abreast Akin Apprehend COMMITTED;mysql> Alpha TRANSACTION;mysql> Baddest CURRENT_TIME();+----------------+| 21:13:51 |+----------------+mysql> Baddest * FROM User Area I... Read More by user

Tutorial Addendum on SQL - Transaction Administration

 Transaction Abreast LevelsAs we can see from antecedent sections, the appulse of a transaction in the accepted session is simple. However, circumstantial affairs in assorted sessions may appulse each additional in some ways. Three phenomena accept been empiric in circumstantial transactions: Dirty Apprehend - One transaction T1 reads uncommitted changes from addition transaction T2. If T2 performs a acknowledgment later, T1 may accept acclimated incorrect datafrom the uncommitted changes.Non-Repeatable Apprehend - One transaction T1 reads a row, which is afflicted and committed by addition transaction T2 later. Now if T1 reads the aforementioned row again,the aftereffect will be will be altered from the first read.Phantom - One transaction T1 reads a set of rows that amuse a condition. Another transaction T2 then inserts some new rows that amuse the samecondition. If T1 repeats the aforementioned read, it will accept some "phantom" rows. To be able to ascendancy and abstain those pheno... Read More by user

Tutorial Addendum on SQL - Transaction Administration

 Here is a simple analysis cipher on the absence transaction: -- Rollback.sql-- Absorb (c) 2004 by Dr. Yang--SET AUTOCOMMIT = 0;USE test;DROP TABLE IF EXISTS User;CREATE TABLE User (Login VARCHAR(8), Countersign CHAR(8)) ENGINE=InnoDB;INSERT INTO User Ethics ( bill , 83BF9598 );COMMIT;INSERT INTO User Ethics ( jack , 8IS3KOXW );ROLLBACK;INSERT INTO User Ethics ( john , FC93846F );COMMIT;INSERT INTO User Ethics ( mike , 86D47E70 );Output: mysqlinmysql testmysql> Baddest * FROM user;+-------+----------+| Login | Countersign |+-------+----------+| bill | 83BF9598 || john | FC93846F |+-------+----------+Observe that:How InnoDB is defined as the accumulator engine for the table.How to about-face off the auto-commit flag.How uncommitted changes can be formed back.Uncommitted changes are formed aback at the end of the session.Here is addition simple analysis cipher on non-default transactions: -- Transaction.sql-- Absorb (c) 2004 by Dr. Yang--SET AUTOCOMMIT = 1;DROP TABLE IF EXISTS User;CREAT... Read More by user

Tutorial Addendum on SQL - Transaction Administration

 This affiliate describes:What is a transaction?How does MySQL abutment of transaction management?What are transaction abreast levels.How does MySQL adumbrate uncommitted changes from additional applicant sessions?How does MySQL supports transaction abreast levels?MySQL transaction abreast akin tests - apprehend uncommitted, apprehend committed, andrepeatable read.All addendum in affiliate are based MySQL 5.0 server.What Is A TransactionTransaction - A arrangement of executions of SQL statements that can be advised as a individual assemblage in which all data changes can be committed or annulled as a whole.Most database servers action two transaction administration modes:Auto Accomplish On: Anniversary SQL account is a transaction. Data changes resulted from anniversary account are automatically committed. Auto Accomplish Off: Affairs are absolutely started and concluded by the applicant program. Data changes are not committed unless requested by the client program.Most database server ... Read More by user

Tutorial Addendum on SQL - Baddest Statements

 GROUP BY Clause"GROUP BY clause" modifies the abject table by alignment aboriginal rows into accumulation rows based on identical accumulated ethics of the defined accumulation columns. In additional words, anniversary consistent row represents a accumulation of aboriginal rows that has a different aggregate of the ethics in the defined accumulation columns. Original columns are bargain to the specifiedgroup columns only. Accumulation rows can aswell be filtered out by a defined condition."GROUP BY clause" syntax is: GROUP BY group_columns [HAVING having_condition]where "group_columns" is a account of columns in the orifginal abject table, and "having_condition" is a assert operation that will aftereffect a true or false condition. Rule 1: Two types of data can be acclimated in baddest expressions: 1. accumulation columns; 2. a accumulation action of any aboriginal columns. Accumulation functions are:COUNT(column): Amount of aboriginal annal in the accumulation represented by this cons... Read More by user

Tutorial Addendum on SQL - Baddest Statements

 JointTable.sql - Archetype of Accompany TablesTo validate the accompany table logics mentioned in the antecedent section, I wrote thefollowing SQL code, JointTable.sql: -- JoinTable.sql-- Absorb (c) 1999 by Dr. Yang---- Creating user tableDROP TABLE IF EXISTS User;CREATE TABLE User (ID INT, Login CHAR(8), Dept_ID INT);INSERT INTO User Ethics (1, ,1);INSERT INTO User Ethics (2, mike ,2);INSERT INTO User Ethics (3, bill ,3);INSERT INTO User Ethics (4, mary ,3);INSERT INTO User Ethics (5, lisa ,5);-- Creating dept tableDROP TABLE IF EXISTS Dept;CREATE TABLE IF NOT EXISTS Dept (ID INT, Name CHAR(16));INSERT INTO Dept Ethics (1, Algebraic );INSERT INTO Dept Ethics (3, Chem );INSERT INTO Dept Ethics (4, Law );INSERT INTO Dept Ethics (5, English );INSERT INTO Dept Ethics (5, Latin );-- Breeding accompany tablesSELECT Active cantankerous accompany AS --- ;SELECT * FROM User Cantankerous Accompany Dept;SELECT Active close accompany AS --- ;SELECT * FROM User Close Accompany Dept ON User.Dept_ID... Read More by user
Tags: column, statements, values, latin, cross

Tutorial Addendum on SQL - Baddest Statements

 Join TablesA accompany table is the achievement table of a accompany operation on two tables. There are several types of joinoperations:1. Cantankerous Accompany - Takes anniversary row in the larboard table, and joins assimilate all rows in the appropriate table.The amount of columns of the achievement table is the amount of columns of the larboard table additional the amount of columns of the appropriate table. The amount of rows of the achievement table is the amount of rows of the larboard table times the amount of rows of the appropriate table. A cantankerous accompany operation is aswell alleged Cartesian artefact operation.There are two means to address a cantankerous accompany table: table_l, table_rtable_l Cantankerous Accompany table_rThe cantankerous accompany operation argumentation can be bidding as: Loop on anniversary row in the larboard table (L) Bend on anniversary row in the appropriate table (R) Accomplish an achievement row with all columns of the accepted row of L ... Read More by user

Tutorial Addendum on SQL - Baddest Statements

 Select StatementsA baddest account is aswell alleged a concern statement. It is commonly acclimated to retrieve rows of data called from defined tables. The all-encompassing syntax of a baddest account is: SELECT select_expression_list [FROM clause]where "expression_list" defines a account of baddest expressions, and"FROM clause" defines a baddest table with rows and columns of values. Cavalcade names ofthe baddest table can be acclimated as variables in baddest expressions to represent cavalcade values in anniversary row.When a baddest account is executed, a nested bend argumentation will be performed to accomplish rows of achievement data: Loop on anniversary row of the baddest table, do: Bend on anniversary baddest expression, do: Appraise this announcement with accessible cavalcade ethics in accepted row of the baddest table. End of loop Acknowledgment the after-effects of all baddest expressions as a row of achievement dataEnd of loopNote:The amount of columns of an achievement ro... Read More by user
Tags: column, operation, statements, condition, group, values, refers, statement, sample, columns

Tutorial Addendum on SQL - MySQL - Stored Action Accent

 CursorsA cursor is a data blazon that represents a affiliation handle to the achievement table of a baddest statement. A cursor is actual agnate to a book handle in some additional programming languages. There are several statements accompanying to the use of a cursor:DECLARE account - To acknowledge a cursor capricious and accessory it to a baddest statement: DECLARE cursor_variable CURSOR FOR select_statement;OPEN account - To assassinate the associated baddest account and set the cursor to point to the first row of the achievement table: OPEN cursor_variable;FETCH account - To back data from the accepted row into accepting variables, and set thecursor to point to the next row of the achievement table: FETCH cursor_variable INTO variable, variable, ...;CLOSE account - To abutting the cursor: CLOSE cursor_variable;When a cursor alcove the end of the achievement table, the Back account will aftereffect in an beheading error: 02000. But this absurdity can be adapted into a analytic acti... Read More by user

Tutorial Addendum on SQL - MySQL - Stored Action Accent

 Below is a sample cipher that uses a while bend to admit assorted rows into a table: -- ProcedureLoop.sql-- Absorb (c) 2004 by Dr. Yang--DROP2 DATABASE IF EXISTS HyTest;CREATE DATABASE HyTest;USE HyTest;--DROP Action IF EXISTS InitTable;DELIMITER / ;CREATE Action InitTable(IN N INTEGER)BEGIN Acknowledge I INTEGER; SET I = 0; WHILE I < N DO Admit INTO MyTable Ethics (I, RAND()*N); SET I = I + 1; END WHILE;END/DELIMITER ; /--DROP TABLE IF EXISTS MyTable;CREATE TABLE MyTable (ID INTEGER, Amount INTEGER);CALL InitTable(100);--SELECT My table: AS --- ;SELECT * FROM MyTable Area ID < 10;Output: My table:ID Value0 31 632 83 524 355 186 867 758 189 63To breach out of the accepted abundance and abide with the next abundance of a LOOP, Echo or WHILE statement, you can use the ITERATE statement: label WHILE condition ...... INTERATE label; ......END WHILE labelTo breach out of the accepted abundance and leave the LOOP, Echo or WHILE statement, you can use the LEAVE statement: label WHILE co... Read More by user
Tags: create, leave, language, database, stored, condition, procedure, statement

Tutorial Addendum on SQL - MySQL - Stored Action Accent

 This affiliate describes:Local variables in stored procedures.Execution breeze ascendancy statements.Cursor accompanying statements.All addendum in affiliate are based MySQL 5.0 server.Local VariablesA stored action can accept bounded variables. To ascertain a bounded variable, you can use the Acknowledge statement: DECLARE capricious data_type [DEFAULT value];To accredit a new amount to a variable, you can use the SET statement: SET capricious = expression;The Baddest account can aswell be acclimated to accredit ethics to variables: SELECT expression, expression, ... INTO variable, variable, ... [FROM clause];Once a capricious is defined, it can be acclimated in any expressions in any statements.Execution Breeze Ascendancy StatementsTo selectively active a accumulation of statements, you can use the IF statement: IF action Then statement_listELSE IF action Then statement_listELSE IF action Then statement_list......ELSE statement_listEND IFTo again active a accumulation of statements a... Read More by user

Tutorial Addendum on SQL - MySQL - Stored Procedures

 Here is a simple analysis on stored action the MySQL applicant tool: mysql> USE test; mysql> DELIMITER / ;mysql> Make Action Msg() -> BEGIN -> Baddest CURRENT_TIME() AS Time; -> Baddest Accost world! As Message; -> END/Query OK, 0 rows afflicted (0.75 sec)mysql> DELIMITER ; /mysql> Alarm Msg();+----------+| Time |+----------+| 17:35:51 |+----------+1 row in set (0.07 sec)+--------------+| Bulletin |+--------------+| Accost world! |+--------------+1 row in set (0.08 sec)Query OK, 0 rows afflicted (0.09 sec)Stored Action ParametersA stored action constant is play the aforementioned role as a action paramter in some other languages. It can be acclimated to canyon data in to and/or out of the stored procedure. Here is how to specify a constant in the make action statement: parameter_type parameter_name data_typewhere parameter_type can be one the following: IN - To announce that this constant is for ascribe data only.OUT - To announce that this constant is for achievement data only.INOUT -... Read More by user

Tutorial Addendum on SQL - MySQL - Stored Procedures

 This affiliate describes:What is a stored procedure?How to make a stored procedure.How to canyon data through parameters.All addendum in affiliate are based MySQL 5.0 server.What Is A Stored Procedures?A stored action is an executable program that is stored in the database server waiting to be alleged for execution. A stored action should be accounting in a programminglanguage that is accurate by the database server. Some database servers action appropriate languages that are continued from the accepted SQL. For example:PL/SQL - Stored action accent for Answer database server.Transact SQL - Stored action accent for MS SQL server. Store action languages usually action you statements to:Receive and acknowledgment data from the calling environment.Declare and use bounded variables.Execute approved SQL statements on the server.Loop through a set of statements assorted times.Conditionally ascendancy the beheading flow.Creating Stored Procedures in MySQLMySQL aswell offers an extention of SQ... Read More by user

Tutorial Addendum on SQL - Operations and Expressions

 Operation ExamplesExample 1 - NumericOps.sql -- NumericOps.sql-- Absorb (c) 1999 by Dr. Yang--SELECT 1 + 2 AS LINE_1;SELECT 2 / 3 AS LINE_2;SELECT 2.0000 / 3 AS LINE_3;SELECT 1234567890/10000 AS LINE_4;SELECT 1234567890/1000000000 AS LINE_5;SELECT 1234567890/1e10 AS LINE_6;SELECT 1234567890/1e13 AS LINE_7;SELECT 1234567890/1e14 AS LINE_8;SELECT 1 / 0 AS LINE_9;SELECT 1.2345 - 0.2345 AS LINE_10;SELECT 2.00 / 1 AS LINE_11;SELECT 2.00 - 1 AS LINE_12;Output: LINE_13LINE_20.67LINE_30.666667LINE_4123456.79LINE_51.23LINE_60.123456789LINE_70.000123456789LINE_81.23456789e-005LINE_9NULLLINE_101.0000LINE_112.0000LINE_121.00Notes:As you can see from the output, the data blazon of the consistent amount depends on the data types of the operands.Line 1 tells us that if both operands are integers and the consistent amount is a accomplished number, the consistent data blazon will be integer. Line 2 and 4 acquaint us that if both operands are integers and the consistent value is not a accomplished numbe... Read More by user
Tags: example, value, operations, string, tells

Tutorial Addendum on SQL - Operations and Expressions

 Predicate OperationsPredicate operations are operations that can be evaluated to accord a action of true or false:1. "Comparison" Predicates: Compares two ethics of the aforementioned blazon according to a predefined order. There are 6 allegory operations:Equal: amount = valueNot Equal: amount <> valueLess Than: amount < valueGreater Than: amount > valueLess Than or Equal: amount <= valueGreater Than or Equal: amount >= value2. "Between" Predicates: Analysis a accustomed amount adjoin a amount range. There are 2 "between" operations:Between: amount Amid amount AND valueNot Between: amount NOT Amid amount AND value3. "In" Predicates: Analysis a accustomed amount adjoin a account of values.There are 2 "in" operations:In: amount IN (value, value, ..., value)Not In: amount NOT IN (value, value, ..., value)4. "Like" Predicates: Analysis a accustomed appearance cord adjoin a characterpattern. By absence "Like" operations are not case sensitive. There are 2 "Like" operations:Like: co... Read More by user

Tutorial Addendum on SQL - Operations and Expressions

 This affiliate describes:Expressions.Arithmetic operations.Predicate operations.Date and time operations.Operation examples.All addendum in affiliate are based on SQL-92 and MySQL server.Value ExpressionsValue Expressions: Syntax forms to accurate operations adjoin data values. SQL divides amount expressions into several categories: numeric expressions, appearance stringexpressions, bit cord expressions, date and time expressions, and time breach expressions.1. Numeric amount expressions are operations that absorb numeric values.Examples: 1 + 12 / 3100 * (1 + 0.05) * (1 + 0.06)2. Appearance cord expressions are operations that absorb appearance strings.Examples: Accost || world! -- Concatenation, not accurate by MySQL3. Bit cord expressions are operations that absorb bit strings.Examples: ~ x 01 -- Negation3. Date and time expressions are operations that absorb data and time values, and time breach values. Examples: date 1999-01-01 + breach 1 year; -- abacus 1 yeartimestamp 1999-01-01 ... Read More by user
Tags: character, value, operations, examples, values, notes, string

Tutorial Addendum on SQL - Addition to MySQL

 To assassinate the statements in hello.sql, you can use the "source" commandinside mysql: mysqlinmysql --host localhost test......mysql> antecedent hello.sqlQuery OK, 0 rows afflicted (0.05 sec)Query OK, 1 row afflicted (0.00 sec)+--------------+| bulletin |+--------------+| Accost world! |+--------------+1 row in set (0.00 sec)Query OK, 0 rows afflicted (0.00 sec)Or you can run mysqsl in accumulation mode: mysqlinmysql --host localhost analysis < hello.sqlmessageHello world!As you can see, this is a abundant bigger way to assassinate SQL statements.So from now on, I will consistently run mysql in accumulation mode.Dumping Data into Files - mysqldumpmysqldump is a apparatus to dump table anatomy and data to files. This apparatus can beused in altered ways.1. Dump tables of a database as SQL statements into a individual file. Table structures will be dumped as make table statements. Data rows will be dumped as admit statements. If table is not specified, all tables will be dumped. ... Read More by user

Tutorial Addendum on SQL - Addition to MySQL

 This affiliate describes:What s in MySQL?How to use the SQL applicant apparatus - mysql.How to dump data into files.How to amount data from files aback to tables.What s in MySQL?Programs and accoutrement offered in MySQL:mysqld - MySQL server daemon.mysqladmin - Ambassador tool, command band based.mysql - SQL applicant tool, command band based.mysqlimport - Apparatus to amount data into tables from argument files. mysqldump - Apparatus to dump data of the an absolute database.mysqlcheck - Apparatus to analysis and adjustment databases. mysqlmanager - SQL applicant tool, GUI based.Using the SQL Applicant Apparatus - mysqlmysql is actual simple to use:To barrage mysql, run "mysqlinmysql --host hostName databaseName".To run any SQL statement, access "sqlStatement;". The endure character, ";", triggers mysql to assassinate the account on the server.To abdicate from mysql, access "quit".To get help, access "help".In the afterward example, I accomplished 4 SQL statements with mysql: mysqli... Read More by user
Tags: create, based, files, world, affected, client, statements, values, message, command, statement

Tutorial Addendum on SQL - Locks And Deadlocks

 We all understand that assorted locks in assorted sessions could couldcause deadlocks. Let s see if we can make a deadlock in MySQL amid two sessions: mysql> Alert >;>DROP TABLE IF EXISTS User;>CREATE TABLE User (ID INT > PRIMARY KEY, Name CHAR(8))> ENGINE=InnoDB; >INSERT INTO User Ethics (2, > bill );>LOCK TABLES User WRITE; c:>mysqlinmysql test mysql> Alert >; >DROP TABLE IF EXISTS System; >CREATE TABLE Arrangement (ID INT > PRIMARY KEY, Name CHAR(8)); >INSERT INTO Arrangement Ethics (2, > atramentous ); >SELECT * FROM User; +----+------+ | 2 | bill | +----+------+ >LOCK TABLE Arrangement WRITE; >SELECT * FROM User; Absurdity Table user was not bound with LOCK TABLESMySQL s behavior on my "SELECT * FROM User" is interesting. It errored out instead of putting the affair into a cat-and-mouse status. I anticipate it is accomplishing thisin adjustment to abstain the achievability of deadlocks. After some added tests, I begin that MySQL s aphorism is actual conservative: If a affair is u... Read More by user

Tutorial Addendum on SQL - Locks And Deadlocks

 This affiliate describes:What are the types and levels of locks?How table akin locks plan in MySQL?How row akin locks plan in MySQL?All addendum in affiliate are based MySQL 5.0 server.Types and Levels of LocksThere are two types of locks:Read Lock - The bound data is aloof for apprehend by the accepted session. Other sessions can apprehend the bound data. But they can not address (update) the bound data.A apprehend lock is aswell alleged a aggregate lock. Write Lock - The bound data is aloof for address by the accepted session.Other sessions can not apprehend and address the bound data. A address lock is aswell alleged an absolute lock.There are three levels of locks:Table Lock - The lock is set at the table level. All rows in the bound table are locked.Row Lock - The lock is set at the row level. Some rows of a table are locked. But additional rows are not locked.Column Lock - The lock is set at the cavalcade level. Some columns of a row are locked.But additional columns are not lock... Read More by user

 

 

Pages :  1 2