| SQL is
a standard computer language for accessing
and manipulating databases.
What is SQL?
- SQL stands for Structured
Query Language
- SQL allows you to access a database
- SQL is an ANSI standard computer
language
- SQL can execute queries against
a database
- SQL can retrieve data from a database
- SQL can insert new records in
a database
- SQL can delete records from a
database
- SQL can update records in a database
- SQL is easy to learn
SQL is a Standard - BUT....
SQL is an ANSI (American National
Standards Institute) standard computer
language for accessing and manipulating
database systems. SQL statements are
used to retrieve and update data in
a database. SQL works with database
programs like MS Access, DB2, Informix,
MS SQL Server, Oracle, Sybase, etc.
Unfortunately, there are many different
versions of the SQL language, but
to be in compliance with the ANSI
standard, they must support the same
major keywords in a similar manner
(such as SELECT, UPDATE, DELETE, INSERT,
WHERE, and others).
Note: Most of the SQL database
programs also have their own proprietary
extensions in addition to the SQL
standard!
SQL Database Tables
A database most often contains one
or more tables. Each table is identified
by a name (e.g. "Customers" or "Orders").
Tables contain records (rows) with
data.
Below is an example of a table
called "Persons":
| LastName |
FirstName |
Address |
City |
| Hansen |
Ola |
Timoteivn
10 |
Sandnes |
| Svendson |
Tove |
Borgvn
23 |
Sandnes |
| Pettersen |
Kari |
Storgt
20 |
Stavanger |
The table above contains three records
(one for each person) and four columns
(LastName, FirstName, Address, and
City).
SQL Queries
With SQL, we can query a database
and have a result set returned.
A query like this:
SELECT LastName FROM Persons |
Gives a result set like this:
| LastName |
| Hansen |
| Svendson |
| Pettersen |
Note: Some database systems
require a semicolon at the end of
the SQL statement. We don't use the
semicolon in our tutorials.
SQL Data Manipulation Language (DML)
SQL (Structured Query Language) is
a syntax for executing queries. But
the SQL language also includes a syntax
to update, insert, and delete records.
These query and update commands together
form the Data Manipulation Language
(DML) part of SQL:
- SELECT - extracts data
from a database table
- UPDATE - updates data in
a database table
- DELETE - deletes data from
a database table
- INSERT INTO - inserts new
data into a database table
SQL Data Definition Language (DDL)
The Data Definition Language (DDL)
part of SQL permits database tables
to be created or deleted. We can also
define indexes (keys), specify links
between tables, and impose constraints
between database tables.
The most important DDL statements
in SQL are:
- CREATE TABLE - creates
a new database table
- ALTER TABLE - alters (changes)
a database table
- DROP TABLE - deletes a
database table
- CREATE INDEX - creates
an index (search key)
- DROP INDEX - deletes
an index
SQL Basic
[SQL
Tutorial] [SQL
Introduction] [SQL
Select] [SQL
Where] [SQL
Insert] [SQL
Update] [SQL
Delete]
SQL Advance
[SQL
Order By] [SQL
AND & OR] [SQL
In] [SQL
Between] [SQL
Aliases] [SQL
Join] [SQL
Union] [SQL
Create] [SQL
Drop] [SQL
Alter] [SQL
Functions] [SQL
Group By] [SQL
Select Into] [SQL
Create View] [SQL
Server]
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