Inner Join vs Outer Join | Know Major 5 Differences

inner join vs outer join

Inner join vs Outer join SQL

Join is a way of merging two and above tables to be a single table. Joined tables are special kinds of relationships that consist of one or extra primary keys. The keys can either be column aliases or primary keys.

An inner-join is normally utilized in joining numerous rows of 2 various tables together with a common key in between them. This has no implicit or explicit columns. When there’s a matching key in between the 2 tables, where inner join combines the 2 or more tables through inserting the key-value as extra into every table, it’s known as outer join. If the database size is important, utilizing a single-table outer-join makes queries performance much better.

In SQL, join is for comparing & combining tables & returns particular rows of information. Inner join gets & returns matching information from the tables, while outer join gets & returns matching information & some dissimilar information from combined details.

Inner Join

Inner join concentrates on the commonality between 2 tables. When utilizing an inner-join, it needs to have some matching information between the tables that are to be compared. Moreover, inner-join looks at tables for overlapping or matching data. When it’s found, inner join joins & returns the data into a single new table.

Inner join syntax

Inner join syntax

Inner Join example

Inner Join example

In table 1 & table 2 above, 2 things are in common. These are Kiwis & Onions. They are common for all tables in the product name. Remember tomatoes & broccoli cannot be included in the Inner join table. The reason being we’re using inner join which returns matching or common values.

SQL Query Example for Inner Join

SQL Query Example for Inner Join

Outer Join

Outer join gives a recordset or rows which include what inner join will return. Moreover, it also contains other rows that have no equivalent match found in a different table.

The 3 kinds of outside joins include;

  • Right Outer-Join (Right Join)
  • Left Outer-Join (Left Join)
  • Full Join (Full Outer-Join)

These outside joins speak of a section of the information that’s being compared, returned, or combined. Other times nulls are produced in the process as other information is mutual while other information isn’t.

Left Join

Here, all the rows of the left table are reserved in outcomes. In case the join rule is met with other tables, the column values are given back. Otherwise, null values will be returned to those columns.

Left outer join syntax

Left outer join syntax

Right Join

Here, all the rows of the right table will be retained in outcomes. In case the join rule is met with other tables, the column values will be returned. Otherwise null values will be returned for the columns.

Right outer join syntax

Right outer join syntax

Full Join

Here, the rows of all tables are changed. If the join condition is met, the columns are populated utilizing the values of all tables. Moreover, if the join rule fails, then the values of any of the tables will be populated in columns & the rest will be populated as nulls.


When you have more joints, both inner & outer joints could take longer to complete. However, the performance level varies depending on database size. Moreover, inner & outer joins can suffer temporary data costs, though the former is expensive the reason being it forms more chances for data loss.  Remember that both of these kinds of joins improve database performance. An inner join will operate better when the number of the tuples is big, & the database is made to support them. When you have 2-tier architecture or you’ve linked database types, the two-table join will operate better.

Terry White

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