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.

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