A Brief Guide to SQL

In this notes I use MySQL for writing all queries. So, make sure to install the MySQL server in your local machine.

Below are the links which may be helpful to you if you are using Ubuntu.

• Installing MySQl
• Databases | MySQL | Commands

In order to understand the fundamentals such as what is SQL? What are the differences between SQL & NoSQL? How to create a database and tables? and for any such questions you can refer to the below links

• SQL Basics

August 21, 2022

Query Mechanics

• Each time a query is sent to the server, the server checks for the permission to execute the statement, permission for accessing the desired data, syntax of your statement.

• If your statement passes these three tests, then your query is handed to the query optimizer, whose job it is to determine the most efficient way to execute your query.

• The optimizer is the set of routines which decide what execution path the DBMS should take for queries. Know more about optimizer code

• There are 6 query clauses in MySQL: select, from, where, group by, having, order by

Select:

• Select is one of the last clauses that the database server evaluates.
• The select clause determines which of all possible columns should be included in the query’s result set.

SELECT DISTINCT column_name 
FROM table_name  
ORDER BY column_name

from:

• The from clause defines the tables used by a query, along with the means of linking the tables together.

Tables: 4 different types

• Permanent Tables
• Derived Tables
• Temporary Tables
• Virtual Tables