Inner Join vs Outer Join

Difference Between Inner Join and Outer Join

A join is used to combine rows from different tables with a common column between them. This column connects the tables to join the rows. If there is a matching column, between two tables while the inner join takes all the entries from both the tables and join them. It can be two tables or more than that. If there is a match in either table, outer join records all the entries and returns the output. The common match can be in right or left tables. Outer join gives the output that larger. Outer join can be left outer join and right outer join.

Head to Head Comparison between Inner Join vs Outer Join (Infographics)

Below are the top 10 comparisons between Inner Join vs Outer Join:

Key differences between Inner Join vs Outer Join

Let us discuss some key differences in the following points:

1. Inner joins work only when there is a matching condition. If any column of both the tables is matching, then inner join will combine the entries. Whereas outer join combines the entries even when there are no matching columns. In this case, the outer join combines all the entries of the column.

2. Outer join will return all the entries of a column even if there are no matching entries. An inner join will drop the column and gives the result without that column.

3. While considering the Venn diagram, the inner join gives the result of the intersection of two tables. Outer join gives the result of the union of two tables. If two tables A and B are considered, an inner join is the intersection of A and B while the outer join is the union of A and B.

4. Inner join does not have any type. Outer join has left outer join, right outer join, and full outer join. Left outer join is used to combine the tables on the left side, the right outer join is used to combine the entries from the right table and full outer join combines the tables entirely.

5. A record with a related ID should exist in the resulting table for inner join. This shows the output with the related data. For outer join, the related ID is not needed. Outer join gives output in a way that the entire table is visible for the full join. This, in turn, gives a larger result.

6. If the records are not matching in the tables, the value is returned as null in Outer Join. If the records are not matching, the entry is not considered in the result for inner join.

7. There should be at least a common entry for inner join from the tables. Common entries are not needed for outer join though if the common entries are there, they need not be avoided.

8. A query is written for both inner and outer joins. In an inner join, the query specifies to match two tables based on the query and if the row from the first table matches the rows from the second table then rows from the second table will be given as output. In outer join, the query specifies the rows of two tables and if there are no match between two tables, then both the tables are returned as output. If there is a match in the table, all entries along with common entry are returned as output.

9. Inner join is considered a simple join which offers result directly. Outer join is a complex join with either left or right or fuller join. The results are not offered as direct.

Comparison Table of Inner Join vs Outer Join

The table below summarizes the comparisons between Inner Join vs Outer Join:

Inner Join	Outer Join
Only common records from both the tables are taken where there is a common ID.	All the entries from the tables are taken and common ID is not required at all.
All the rows or entries will have values as it is taken from the tables with common entries.	All the rows or entries will not have values and return null value as tables with common ID is not necessary.
There are no variants for inner join.	Outer join can be left outer or right outer join.
Optimizer can be used in inner join as it gives many options.	The use of optimizer is limited as the joins take all the entries and its usage is not feasible.
Inner join is the common join and is used judiciously. The results provided have least entries and in most cases, will be able to update the requirement of the user.	Outer join has many options such as left and right join and hence its usage must be monitored and the results must be checked thoroughly.
Inner joins are slower and the performance is not up to the mark.	Outer joins, especially left outer joins are faster and perform well in most cases.
A condition is given in the inner join query and it is necessary to satisfy the same.	A condition is not given in the outer join query and they need not match any conditions.
If the rows in table A does not have any matching entries in table B, then those entries are not considered for output in the inner join.	If the rows in table A does not have any matching entries in table B, then the output will return null values.
If there is a match in either table, it will not consider for left or right tables. The result is given right away.	If there is a match in tables, it will check either the condition whether it is given for left or right tables. If the condition is given, the entry is considered accordingly. If no conditions are given, then the full outer join is the output for the same.
If a related data entry should exist as per the customer requirement or database design, use inner join.	If a related data entry existence is not necessary, as per the customer requirement or database design, use outer join.

Conclusion

Based on the data needed to be represented in the table, use the joins. Also, consider the performance and understanding of the joins. While left join returns common values from the left table and all entries from the right table, right join does the opposite of left join. If you need all the entries, go with a full outer join.

Recommended Articles

This is a guide to the top difference between Inner Join vs Outer Join. Here we also discuss the key differences with infographics and comparison table. You may also have a look at the following articles to learn more –

1. Introduction to Inner Join in Oracle
2. How does Cross Join Work in Oracle?
3. Overview of Types of Joins in SQL Server
4. Joins in Hive With Different Commands
5. Examples of SQL Right Join
6. Guide to QlikView Left Join
7. Complete Guide to PostgreSQL Cross Join
8. LEFT OUTER JOIN in PostgreSQL | Examples
9. BETWEEN in Oracle | Syntax and Examples