An inner join:
Uses a comparison operator (=, <>, <, <=, >, or >=) to match rows from two tables based on the values in common columns from each table. You can retrieve all rows in which the author identifier (the column au_id) is the same in both the tables authors and title_authors, for example.
Returns a result that contains only joined rows that satisfy the join condition(s).
Is the most common type of join; I’ll give many examples.
SELECT columns FROM table1 INNER JOIN table2 ON join_conditions