What is Relational Database
A database
relation is a predefined row/column format for storing information in a
relational database.
Relations are
equivalent to tables.
Definition of
DBMS terms
a.
SQL is
structured Query Language
What is SQL?
SQL acronyms of structured Query Language, it’s a computer language use for storing, manipulating and retrieving data stored in relational database. SQL is a language of database, it includes database creation, deletion, fetching rows and modifying rows etc.
SQL is an ANSI
(American National Standards Institute standard but there are many different
versions of the SQL language.
SQL is the standard language for Relation Database System. All relational database management systems like MySQL, MS Access, Oracle, Sybase, Informix, postgres and SQL Server uses SQL as standard database language.
SQL COMMANDS
The standard SQL commands to interact with relational databases are CREATE, SELECT, INSERT, UPDATE, DELETE, and DROP. These commands can be classified into groups based on their nature as: DML, DCL, and DQL
b.
DML: Data
Definition Language:
Data
are manipulated by using: INSERT, UPDATE and DELETE command.
INSERT: This command is
use to create record.
UPDATE: This Command
is use in modifying records.
DELETE: Deletes records.
c. DCL-Data Control Language:
GRANT: gives a privileges to user
REVOKE: Takes back privileges granted from user.
d. DQL: Data Query Language
Uses SELECT commands: retrieves certain records from one or more tables.
e. ALTER: Modifies an existing database object, such as a table.
f. DROP: Deletes an entire table, a view of a table or other object in the database.
CREATING OF SQL
DBASE
CREATE DATABASE using SQL
The SQL CREATE
DATABASE statement is used to create new SQL database.
SYNTAX:
basic syntax of CREATE DATABASE statement is as follows:
CREATE DATABASE
DatabaseName;
Always database
name should be unique within the RDBMS.
Example:
If you want to
create new database <School>, then CREATE DATABASE statement would be as
follows:
SQL> CREATE
DATABASE School;
Make sure you have administrative privilege before creating any database. Once a database is created, I you can check it in the list of databases as follows SQL> SHOW DATABASES
DATA
MANIPULATION LANGUAGE
CREATE TABLE
Creating a basic
table involves naming the table and defining its columns and each column's data
type.
The SQL CREATE
TABLE statement is used to create a new table.
Syntax:
Basic syntax of
CREATE TABLE statement is as follows:
CREATE TABLE
table_name(
Column 1
datatype,
Column 2
datatype,
Column 3
datatype,
Column N
datatype,
PRIMARY KEY (one
or more columns));
Example: The following
is an example which create a CCUSTOMERS table with ID as primary key and NOT
NULL are the constrains showing that these fields cannot be NULL while creating
records in this table:
SQL> CREATE
TABLE CUSTOMER(
ID INT NOTNULL,
NAME VARCHAR(20)
NOTNNULL,
AGE INT NOTNULL,
ADDRESS CHAR(25),
SALARY DECIMAL(18,2),
PRIMARY KEY (ID));
DROP OR DELETE DATABASE
The SQL DROP DATABASE statement is used to drop
any existing database in SQL schema.
SYNTAX
Basic syntax of
Drop Database statement is a follows:
DROP DATABASE
DatabaseName;
UDATE
The
SQL Update query is used to modify the existing records in a table you use
WHERE clause with UPDATE query to update selected rows otherwise all the rows
would be affected.
SYNTAX
The
basic syntax of UPDATE query with WHERE clause is as follows:
UPDATE
table_name
SET
column1=value1,clumn2-=value2….,, columnN=valueN
WHERE[condition];
Example:
following is an example which would update ADDRESSfor a customer whose ID is 6:
SQL>
UPDATE CUSTOMERS
SET
ADDRESS = ‘Pune’
WHERE ID =6;