What Is Outer Join?

One way to join data from many tables in SQL is through an outer join. It's like attempting to complete a puzzle with some of the pieces missing. A missing piece may be completed with the use of an outside join. Left outer join, right outer join, and full outer join are the three varieties of outer joins available in SQL. Consider the case where you wish to do an outside join on two tables, A and B. By using a left outer join, we may get back not only the rows that exist in table A but also the rows that exist in table B if they are a match. If there are no matching rows in table B, then the values for those columns in table B will be returned as NULL. Since the rows from table A are on the "left" side of the join, the operation is known as a left outer join. Using a right outer join, we can get back not only the rows that match from table A but also all of the rows from table B. Returning NULL for the columns from table A if there are no matching rows in table A is the expected behavior. In a right outer join, rows from table B are on the "right" side of the join, hence the name. If you did a full outer join between tables A and B, you'd get back not only the rows that match but also all the rows from both tables. If there are no corresponding rows, then the values for the other table's fields will be returned as NULL. A full outer join retrieves every row from both tables, hence the name. When you need to include rows from both tables, even if there are no matching rows, an outside join may be the way to go. Even if some customers only appear in one table, you can use an outer join to build a report containing all customers from tables A and B. That is a very brief introduction to outer joins in SQL. They allow you to incorporate rows from both tables, even when there are no matching rows, and are used to merge rows from two or more tables. Outer joins can be either left, right or entire.