There are four types of JOINs, today I will briefly describe about these categories.

N.B: This is from my personal note, if you have any confusion please let me know.

The Four different types of JOINs

(INNER) JOIN: It will display the matching values in both tables.
FULL (OUTER) JOIN: It will show all records that match either left or right table records.
LEFT (OUTER) JOIN: Select records from the first (left-most) table with matching right table records.
RIGHT (OUTER) JOIN: Select records from the second (right-most) table with matching left table records.

Example

Suppose we have three table Customer,Order and Supplier

Customer                           Order                                 Suplier
-----------------------           -----------------------------          -----------------------
id ---> (Primary key)             order_id ---> (Primary key)            id ---> (Primary key) 
custmer_name                      ooder_numbner                          company_namne
city                              order_date                             city
country                           customer_id--->(foreign key)           country
phone                             order_notes                            phone
                                  total_amount

comparing these three tables i will describe the four types of SQL join,

Here are some questions and it will solve using the four types of SQL joins

Problem 1: Display all the customers name,city their order and order notes in 10th may 2020.-->(Inner Join)
Problem 2: List all customers and the total amount they spent irrespective whether they placed any orders or not.--->           (Left Join)
Problem 3: List customers that have not placed orders. --->(Right Join)
Problem 4: Match all customers and suppliers by country.--->(Full Join)

for the above question SQL codes are written, with this information you can learn about SQL Join easily.