MYSQL,RDBMS

• things which make thing easy
• Ex.
• creating table in mysql

CREATE TABLE student(
student_id INT,
name VARCHAR(20) NOT NULL,
subject VARCHAR(20) /////DEFAULT 'undefined'///UNIQUE/////AUTO INCREMENT,

PRIMARY KEY(student_id)///important to mention

);
/////inserting data/////
SELECT * from student;
INSERT INTO student VALUES(1,'rahul','math');
INSERT INTO student VALUES(2,'aaditya','English');
INSERT INTO student VALUES(3,NULL,'biology');//error --->name should not be null
INSERT INTO student(student_id,name) VALUES(4,'rajesh');--->for specific use

• '*' this symbol is used to select all the data from database

Ex. select * from student;

for specific use 
Ex. select major, name
from student
order by name/////name desc;////asc (ascending)


not equal---->     '< >'

Projection is unary operator it is used to list it returns arguments which are specific to it

•It yields a vertical subset of its argument Relation. Since a relation is a set, any duplicate rows are eliminated.

the join helps to combine multiple tables based on a common field. There are three types of joins THETA JOIN, NATURAL JOIN and EQUIJOIN. 

Active Database

It is a database that driven by ECA(Event condition Action) rules which can respond inside and outside of the database.

possible uses in security,monitoring,alerting and statistic

Event condition Action

Event --> signal that trigger for invocation of rule

Condition -->it is part of logical test if satisfied then evaluated as true, cause the action to be carried out.

Action---->it consist of updation or invocation on local data

Detuctive Database

Database + inference = deductive database

By evaluating rules against the facts new facts can be derived which in turn can be used to answers the queries. it makes database more powerful.