A detailed Guide on sql query Optimization This article was published as a part of the

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A Detailed Guide on SQL Query Optimization
This article was published as a part of the 
Data Science Blogathon
Overview of SQL Query Optimization
SQL
Query optimization is defined as the iterative process of enhancing the performance of a query in
terms of execution time, the number of disk accesses, and many more cost measuring criteria. Data is an
integral part of any application. Access to the data should be in the fastest way possible to enhance the
user experience while using the application.
It is a very critical task. Even slight changes in SQL queries can improve performance drastically. There is
no step-by-step guide for the same. In turn, we must use general guidelines for writing queries, which
operators to use. Then check for execution plans and find out hat part of the query takes the most time
and rewriting that part in some other way.
In this tutorial we will learn the following topics:
SQL Query optimization
Introduction to SQL
Query processing
Purpose of SQL Query optimization
Database for the tutorial
Metrics for analyzing SQL query performance
Optimization techniques
Indexing
Selection
Avoid using SELECT DISTINCT
Inner joins versus WHERE clause
LIMIT command
IN versus Exists
Loops versus Bulk INSERT/UPDATE
Conclusion
Introduction to SQL
SQL(Structured Query Language) is a standard language for accessing, storing, creating, deleting
databases, and perform all other data-related operations. There are four types of language in SQL:
1. DDL(Data Definition Language) 
BE G I NNE R
D ATA E NG I NE E RI NG
SQL

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This includes commands for creating and altering the schema of the database. Example: CREATE, DROP,
ALTER, TRUNCATE.
2. DML(Data Manipulation Language)
This includes commands for updating the data in the database. It alters the instance of the relation. For
example, SELECT, UPDATE, INSERT, DELETE.
3. DCL(Data Control Language)
This includes commands for access to the database. For example, GRANT, REVOKE.
4. TCL(Transaction Control Language)
This includes the commands used to manage transactions in the database. For example, COMMIT,
ROLLBACK.
Image Source: 
Google images
Before going towards the main topic of SQL Query optimization, let us first understand the actual
processing of query:

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