SQL

Database Management Systems

A software program that helps to create , read , update and delete information in a database.

Types of Database Systems

1. Relational DB ( SQL) - example mariaDB , Oracle , MySQL , postgres

   • Stores information in tables in forms of rows and columns
   • Use Structured Query Language for interaction with Database

2. Non Relational DB ( noSQL ) - Redis , MongoDB , Document DB

   • Stores information in the form, of key value pair like in Redis or json as in MongoDB or graph format as in neoj
   • No standard language like SQL for relational DB

3. Primary Key uniquely identifies the row in a table.

4. Surrogate PK does not have validity in real world and applicable only w.r.t table like auto generated id

5. Real PK has validity in real world like email id or ssn number

6. foreign KEY FK identifies the PK of another table in a database and establish the relation ship between tables

7. Composite PK consists of two or more columns uniquely represent PK