Clausulas sql

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SQL Tutorial Tutorialspoint.com
SQL is a database computer language designed for the retrieval and management of data in relational database. SQL stands for Structured Query Language. This tutorial gives an initial push to start you with SQL. For more detail kindly check tutorialspoint.com/sql This SQL tutorial gives unique learning on Structured QueryLanguage and it helps to make practice on SQL commands which provides immediate results. SQL is a language of database, it includes database creation, deletion, fetching rows and modifying rows etc. SQL is an ANSI (American National Standards Institute) standard but there are many different versions of the SQL language.

What is SQL?
SQL is structured Query Language which is a computer language forstoring, manipulating and retrieving data stored in relational database. SQL is the standard language for Relation Database System. All relational database management systems like MySQL, MS Access, Oracle, Sybase, Informix, postgres and SQL Server uses SQL as standard database language. Also they are using different dialects, Such as:

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MS SQL Server using T-SQL, Oracle using PL/SQL, MSAccess version of SQL is called JET SQL (native format )etc

Why SQL?
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Allow Allow Allow Allow Allow Allow Allow users to access data in relational database management systems. users to describe the data. users to define the data in database and manipulate that data. to embed within other languages using SQL modules, libraries & pre-compilers. users to create and drop databasesand tables. users to create view, stored procedure, functions in a database. users to set permissions on tables, procedures, and views

History:
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1970 -- Dr. E.F. "Ted" of IBM is known as the father of relational databases. He described a relational model for databases. 1974 -- Structured Query Language appeared. 1978 -- IBM worked to develop Codd's ideas and released a product namedSystem/R. 1986 -- IBM developed the first prototype of relational database and standardized by ANSI. The first relational database was released by Relational Software and its later becoming Oracle.

SQL Process:
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When you are executing an SQL command for any RDBMS, the system determines the best way to carry out your request and SQL engine figuresout how to interpret the task. There are various components included in the process. These components are Query Dispatcher, Optimization engines, Classic Query Engine and SQL query engine etc. Classic query engine handles all non-SQL queries but SQL query engine won't handle logical files. Following is a simple digram showing SQL Architecture:

SQL Commands:
The standard SQL commands to interactwith relational databases are CREATE, SELECT, INSERT, UPDATE, DELETE, and DROP. These commands can be classified into groups based on their nature:

DDL - Data Definition Language:
Command CREATE ALTER DROP Description Creates a new table, a view of a table, or other object in database Modifies an existing database object, such as a table. Deletes an entire table, a view of a table or otherobject in the database.

DML - Data Manipulation Language:
Command INSERT Creates a record Description

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UPDATE DELETE Modifies records Deletes records

DCL - Data Control Language:
Command GRANT REVOKE Gives a privilege to user Takes back privileges granted from user Description

DQL - Data Query Language:
Command SELECT DescriptionRetrieves certain records from one or more tables

SQL –Syntax
SQL is followed by unique set of rules and guidelines called Syntax. This tutorial gives you a quick start with SQL by listing all the basic SQL Syntax: All the SQL statements start with any of the keywords like SELECT, INSERT, UPDATE, DELETE, ALTER, DROP, CREATE, USE, SHOW and all the statements end with a semicolon (;). Important...