LEFT JOIN vs. LEFT OUTER JOIN in SQL Server

Question

What is the difference between LEFT JOIN and LEFT OUTER JOIN?

Answer 1

To answer your question there is no difference between LEFT JOIN and LEFT OUTER JOIN, they are exactly same that said...

At the top level there are mainly 3 types of joins:

1. INNER
2. OUTER
3. CROSS

---

1. INNER JOIN - fetches data if present in both the tables.

2. OUTER JOIN are of 3 types:

   1. LEFT OUTER JOIN - fetches data if present in the left table.
   2. RIGHT OUTER JOIN - fetches data if present in the right table.
   3. FULL OUTER JOIN - fetches data if present in either of the two tables.

3. CROSS JOIN, as the name suggests, does [n X m] that joins everything to everything.
   Similar to scenario where we simply lists the tables for joining (in the FROM clause of the SELECT statement), using commas to separate them.

---

Points to be noted:

• If you just mention JOIN then by default it is a INNER JOIN.
• An OUTER join has to be LEFT | RIGHT | FULL you can not simply say OUTER JOIN.
• You can drop OUTER keyword and just say LEFT JOIN or RIGHT JOIN or FULL JOIN.

---

For those who want to visualise these in a better way, please go to this link: A Visual Explanation of SQL Joins