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Introduction to SQL
SQL is a standard language for accessing and manipulating databases.
What is SQL?
• SQL stands for Structured Query Language
• SQL lets you access and manipulate databases
• SQL is an ANSI (American National Standards Institute) standard
What Can SQL do?
• SQL can execute queries against a database
• SQL can retrieve data from a database
• SQL can insert records in a database
• SQL can update records in a database
• SQL can delete records from a database
• SQL can create new databases
• SQL can create new tables in a database
SQL DML and DDL
SQL can be divided into two parts: The Data Manipulation Language (DML) and the Data Definition
Language (DDL).
The query and update commands form the DML part of SQL:
• SELECT - extracts data from a database
• UPDATE - updates data in a database
• DELETE - deletes data from a database
• ISERT ITO - inserts new data into a database
The DDL part of SQL permits database tables to be created or deleted. It also define indexes (keys), specify
links between tables, and impose constraints between tables. The most important DDL statements in SQL
are:
• CREATE DATABASE - creates a new database
• ALTER DATABASE - modifies a database
• CREATE TABLE - creates a new table
• ALTER TABLE - modifies a table
• DROP TABLE - deletes a table
• CREATE IDEX - creates an index (search key)
• DROP IDEX - deletes an index
The SQL SELECT Statement
The SELECT statement is used to select data from a database. The result is stored in a result table, called the
result-set.
SQL SELECT Syntax
SELECT column_name(s)
FROM table_name
and
SELECT * FROM table_name
ote: SQL is not case sensitive. SELECT is the same as select.
