Category Archives: DBMS

Posts for Database Management Systems.

Basic SQL Injection and Mitigation with Example

SQL injection is a code injection technique, used to attack data driven applications, in which malicious SQL statements are inserted into an entry field for execution (e.g. to dump the database contents to the attacker). SQL Injection can be used in a range of ways to cause serious problems. By levering SQL Injection, an attacker… Read More »

SQL Interview Questions

What is SQL? SQL stands for Structured Query Language. It is a language used to interact with the database, i.e to create a database, to create a table in the database, to retrieve data or update a table in the database etc. SQL is an ANSI(American National Standards Institute) standard. Using SQL, we can do… Read More »

SQL | Functions (Aggregate and Scalar Functions)

For doing operations on data sql has many built-in functions, they are categorised in two categories and further sub-categorised in different seven functions under each category. The categories are: Aggregate functions: These functions are used to do operations from the values of the column and a single value is returned. AVG() COUNT() FIRST() LAST() MAX()… Read More »

SQL | Date functions

In SQL, dates are complicated for newbies, since while working with database, the format of the date in table must be matched with the input date in order to insert. In various scenarios instead of date, datetime (time is also involved with date) is used. In MySql the default date functions are: NOW(): Returns the… Read More »

SQL | Views

Views in SQL are kind of virtual tables. A view also has rows and columns as they are in a real table in the database. We can create a view by selecting fields from one or more tables present in the database. A View can either have all the rows of a table or specific… Read More »

SQL | GROUP BY

The GROUP BY Statement in SQL is used to arrange identical data into groups with the help of some functions. i.e if a particular column has same values in different rows then it will arrange these rows in a group. Important Points: GROUP BY clause is used with the SELECT statement. In the query, GROUP… Read More »

SQL | Comments

As is any programming languages comments matter a lot in SQL also. In this set we will learn about writing comments in any SQL snippet. Comments can be written in the following three formats: Single line comments. Multi line comments In line comments

SQL | Constraints

Constraints are the rules that we can apply on the type of data in a table. That is, we can specify the limit on the type of data that can be stored in a particular column in a table using constraints. The available constraints in SQL are: NOT NULL: This constraint tells that we cannot… Read More »

SQL | DROP, TRUNCATE

DROP DROP is used to delete a whole database or just a table.The DROP statement destroys the objects like an existing database, table, index, or view. A DROP statement in SQL removes a component from a relational database management system (RDBMS). Syntax: DROP object object_name Examples: DROP TABLE table_name; table_name: Name of the table to be… Read More »

SQL | CREATE

There are two CREATE statements available in SQL: CREATE DATABASE CREATE TABLE CREATE DATABASE A Database is defined as a structured set of data. So, in SQL the very first step to store the data in a well structured manner is to create a database. The CREATE DATABASE statement is used to create a new… Read More »

SQL | Join (Cartesian Join & Self Join)

SQL| JOIN(Inner, Left, Right and Full Joins) In this article, we will discuss about the remaining two JOINS: CARTESIAN JOIN SELF JOIN Consider the two tables below: StudentCourse CARTESIAN JOIN: The CARTESIAN JOIN is also known as CROSS JOIN. In a CARTESIAN JOIN there is a join for each row of one table to every… Read More »