Introduction to Structured Query Language

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The main drive behind a relational data base is to increase precision by increasing the performance with which information is saved. For example, the names of each of the many individuals who immigrated to the U. S. through Ellis Island at the turn of the 20th century were documented by hand on large sheets of paper; individuals from the city of London had their nation of source joined as England, or Great England, or U. s. Empire, or U.K., or UK, or Engl., etc.

SQL allows customers to gain access information in relational data base management techniques, such as Oracle, Sybase, Informix, Microsoft SQL Server, Access, and others, by allowing customers to explain the information the user wants to see. SQL also allows customers to determine the information in a data base, and operate that information.

This website will explain how to use SQL, and give illustrations. The SQL used in this article is “ANSI”, or standard SQL, and no SQL features of specific data source control techniques will be mentioned until the “Nonstandard SQL” section.

Structured Query Language

SQL, which is an acronym for Structured Query Language, is a language to request information from a knowledge source, to add, upgrade, or remove information within a knowledge source, or to control the meta-data of the facts source.

SQL is a declarative language in which the expected result or function is given without the particular information regarding how to work. The steps required to operate SQL statements are managed transparently by the SQL information source. Sometimes SQL is recognized as non-procedural because step-by-step ‘languages’ generally require the facts of the functions to be specified, such as buying and selling platforms, running and searching indices, or eliminating buffers and writing information to filesystems. Therefore, SQL is considered to be designed at a higher conceptual stage of function than step-by-step ‘languages’ because the lower stage logical and physical functions aren’t specified and are determined by the SQL engine or server process that carries out it.

Instructions are given in the form of statements, including a particular SQL declaration and additional factors and operands that apply to that declaration. SQL statements and their modifiers are based upon formal SQL requirements and certain additions to that each database provider utilizes. Commonly used statements are categorized into the following categories:

Data Query Language (DQL)

SELECT – Used to recover certain information from one or more platforms.

Data Manipulation Language (DML)

INSERT – Used to build a record.

UPDATE – Used to change certain information.

DELETE – Used to remove certain information.

Data Definition Language (DDL)

CREATE – Used to build a new table, a perspective of a table, or other item in database.

ALTER – Used to alter a preexisting information source item, such as a table.

DROP – Used to remove an entire table, a perspective of a table or other item in the facts source.

Data Control Language (DCL)

GRANT – Used to give a benefit to someone.

REVOKE – Used to take back rights provided to someone.

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