Page 477 - Computer_Science_F5

Computer Science SQL commands Example context: “If a table needs to
There are five fundamental command
categories, in SQL language, a standard
language for managing and manipulating
databases. These command categories
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are Data Definition Language (DDL)
commands, Data Manipulation Language
(DML) commands, Data Query Language
(DQL), Data Control Language (DCL)
and Transaction Control Language
(TCL). It is crucial to keep the following
considerations in mind before diving into
SQL:
(a) SQL statement starts with SQL
command and ends with a semicolon
(;);
(b) SQL statements are case insensitive,
which means they can be written
using upper, lower, or mixed cases.
But it is a common practice to write
out SQL keyword commands in all
upper cases;
(c) Using SQL, you can perform most
of the actions in a database; and
(d) SQL data types are critical because
they tell the database what type of
data to expect. Common data types
include:
(i) INT: An integer number.
(ii) VARCHAR: Variable-
length strings. For example,
VARCHAR(255) can store
strings up to 255 characters.
(iii) TEXT: For long texts.
(iv) DATE/TIME: For dates and
times.
(v) FLOAT/DOUBLE: For floating-
point numbers.
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Computer Science Form 5.indd 468
store people’s names and their ages, you
would use VARCHAR for names and
INT for ages.”
Data Definition Language (DDL)
commands
DDL commands change the database’s
structure, for example, by creating a table,
deleting a table, and altering a table. DDL
has the following commands: CREATE,
ALTER, DROP, and TRUNCATE.
(a) CREATE
The CREATE command is used to create
a new database or table in the database.
It has the following syntax: CREATE
DATABASE database_name; for the
database and CREATE TABLE table_
name (column_name datatypes [,]); for
the table. The database must be created
first then, followed by the tables;
Example:
CREATE DATABASE student;
CREATE TABLE student_registration (
StudentID int,
FirstName varchar (255),
MiddleName varchar (255),
LastName varchar (255),
Address varchar (255)
);
To create a database and table resulting
from this example, select SQL to
continue with the code and type the
code; first, you need to create a database
and then the table as indicated in Figure
8.19 this is because the table shall belong
to the database.
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