Download Information Technology Module for Managers Structured Query

Information Technology Module for Managers
Structured Query Language (SQL)
Lesson 3
SQL is not itself a database management system, nor is it a stand alone product. You
cannot go into a computer store and “buy SQL”. Instead, SQL is an integral part of a
database management system, a language and tool for communicating with the DBMS.
SQL acts as a „glue‟ that links them together.
The database engine is the heart of the DBMS, responsible for actually structuring,
storing and retrieving the data on the disk. It accepts SQL requests from other DBMS
components, such as a forms facility, report writer, or interactive query facility, from user
written application programs, and even from other computer systems. SQL plays many
different roles:
SQL is an interactive query language. Users type SQL commands into an interactive
SQL program to retrieve data and display it on the screen, providing a convenient, easy to
use tool for ad hoc database queries.
SQL is database programming language. Visual Basic Programmers embed SQL
commands into their application programs to access the data in a database. Both user
written programs and database utility programs (such as report writers and data entry
tools) use this technique for database access.
SQL is a database administration language. The database administration responsible
for managing a minicomputer or mainframe database uses SQL to define the database
structure and control access to the stored data.
SQL is a client/server language. Personal computer programs use SQL to communicate
over a local area network with database servers that store shared data. Many new
applications are using this client/server architecture, which minimizes network traffic and
allows both PCs and servers to do what they do best.
SQL is a distributed database language. Distributed database management systems use
SQL to help distribute data across many connected computer systems. The DBMS
software on each system uses SWQ: to communicate with the other systems, sending
requests for data access.
SQL is a database gateway language. In a computer network with a mix of different
DBMS products, SQL is often used in a gateway that allows one brand of DBMS to
communicate with another brand.
SQL has thus emerged as a useful, powerful tool for linking people, computer programs,
and computer systems to the data stored in a relational database.
Information Technology Module for Managers
Structured Query Language (SQL)
Lesson 3 (contd)
SQL allows end users to extract information themselves, even if they don‟t have any
programming knowledge. SQL is English-like, easy-to-learn query language that
specifies the operations to be performed against the database.
What is SQL?
 Structured Query Language
 Pronounced either “S-Q-L” or “Sequel”
 Originally developed by IBM in mid-1970s
 An international standard language for managing data stored in a relational
database.
 The most common standard is referred to as ANSI SQL-92 (latest version of the
standard is SQL-2003 standardized by ANSI/ISO)
SQL Command Classification
• Data Definition Language (DDL)
–
•
Data manipulation language (DML)
–
•
Commands that define a database, including creating, altering, and
dropping tables and establishing constraints
Provides basic data manipulation operations on data held in the database
Control Language (DCL)
–
Commands that control a database, including administering privileges and
committing data
Common SQL Commands
 Data Definition Language (DDL):
 Create
 Drop
 Alter
 Data Manipulation Language (DML):
 Rename
 Select
 Update
 Insert
 Delete
 Data Control Language (DCL): (not needed for this course)
 Grant
 Revoke