Источник: sql-join.com

INNER JOIN

Select all records from Table A and Table B, where the join condition is met.

LEFT (Outer) JOIN

Select all records from Table A, along with records from Table B for which the join condition is met (if at all).

RIGHT JOIN

Select all records from Table B, along with records from Table A for which the join condition is met (if at all).

FULL JOIN

Select all records from Table A and Table B, regardless of whether the join condition is met or not.

Example

Let’s use the tables we introduced in the “What is a SQL join?” section to show examples of these joins in action. The relationship between the two tables is specified by the customer_id key, which is the “primary key” in customers table and a “foreign key” in the orders table:

Table 1

customer_id	first_name	last_name	email	address	city	state	zipcode
1	George	Washington	[email protected]	3200 Mt Vernon Hwy	Mount Vernon	VA	22121
2	John	Adams	[email protected]	1250 Hancock St	Quincy	MA	2169
3	Thomas	Jefferson	[email protected]	931 Thomas Jefferson Pkwy	Charlottesville	VA	22902
4	James	Madison	[email protected]	11350 Constitution Hwy	Orange	VA	22960
5	James	Monroe	[email protected]	2050 James Monroe Parkway	Charlottesville	VA	22902

Table 2

order_id	order_date	amount	customer_id
1	@July 4, 1776	234.56	1
2	@March 14, 1760	78.5	3
3	@May 23, 1784	124	2
4	@September 3, 1790	65.5	3
5	@July 21, 1795	25.5	10
6	@November 27, 1787	14.4	9