DBMS_SQL_Overview

DBMS 1

--> About DBMS

--> ER Diagram , Entity Set , Relationship , Cardinality Constraint , Attributes , Constraints

--> Keys

--> Functional Dependency

--> Decomposition of a Relation

--> Types of Decomposition

#DBMS 2 --> Normalization

--> Transaction

--> Acid properties

--> Schedules

--> Relational Algebra

#DBMS 3 --> SQL

--> DDL , DML , DCL

--> SQL queries

--> TCL { Commit , rollbacks }

SQL QUERIES

--> SELECT STATEMENT

Deadlocks (Important):

A situation where a set of processes are blocked because each process is holding a resource and waiting for another resource acquired by some other process. Deadlock can arise if following four conditions hold simultaneously (Necessary Conditions):

1. Mutual Exclusion – One or more than one resource is non-sharable (Only one process can use at a time).
2. Hold and Wait – A process is holding at least one resource and waiting for resources.
3. No Preemption – A resource cannot be taken from a process unless the process releases the resource.
4. Circular Wait – A set of processes are waiting for each other in circular form.

● Methods for handling deadlock: There are three ways to handle deadlock

1. Deadlock prevention or avoidance : The idea is to not let the system into a deadlock state.
2. Deadlock detection and recovery : Let deadlock occur, then do preemption to handle it once occurred.
3. Ignore the problem all together : If deadlock is very rare, then let it happen and reboot the system. This is the approach that both Windows and UNIX take.