SQL

difference between outer join and inner join sql

In SQL, a join is used to compare and combine — literally join — and 
return specific rows of data from two or more tables in a database.
An inner join finds and returns matching data from tables,
while an outer join finds and returns matching data and some dissimilar 
data from tables

INNER JOIN : 
The inner join will keep only the information from the two joined tables 
that is related.

OUTER JOIN: 
There are three types of outer joins:
Left Outer Join (or Left Join)
Right Outer Join (or Right Join)
Full Outer Join (or Full Join)

difference between left outer join and left join in sql

There really is no difference between a LEFT JOIN and a LEFT OUTER JOIN. 
Both versions of the syntax will produce the exact same result in PL/SQL.
Some people do recommend including outer in a LEFT JOIN clause so it's 
clear that you're creating an outer join, but that's entirely optional