Inner Join in SQL vs. Outer Join in SQL — What's the Difference?
By Tayyaba Rehman & Urooj Arif — Published on February 2, 2024
Inner Join in SQL combines rows from different tables based on a related column, showing only matching rows. Outer Join shows matching rows plus non-matching rows from one or both tables.
Difference Between Inner Join in SQL and Outer Join in SQL
Table of Contents
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Key Differences
Inner Join in SQL is used to merge rows from two or more tables based on a related column they share, displaying only the rows where there is a match in both tables. Conversely, Outer Join in SQL can be of three types: left, right, or full. It not only shows the matching rows but also displays the non-matching rows from either one table (left or right) or both tables (full).
An Inner Join in SQL provides a result set that includes rows from both tables where the join condition is met. It's commonly used when data needs to be combined strictly based on common attributes. On the other hand, an Outer Join in SQL, particularly a left outer join, will include all rows from the left table and matched rows from the right table, adding NULLs where there's no match.
Inner Join in SQL is more restrictive as it filters out rows that do not have a corresponding match in the other table. This makes it ideal for queries where only complete matches across tables are desired. In contrast, an Outer Join in SQL, especially a right outer join, displays all rows from the right table and the matched rows from the left table, with NULLs for unmatched rows from the left table.
In terms of data completeness, Inner Join in SQL might lead to loss of data if there are no matching rows in the joined tables. This is essential for precise data correlation. Outer Join in SQL, particularly full outer join, merges all rows from both joined tables, filling in with NULLs where there’s no match, ensuring no data is lost from either table.
Usage-wise, Inner Join in SQL is typically used in scenarios where data integrity is crucial and only complete data sets from both tables are required. Outer Join in SQL is more suited for exploratory data analysis or cases where it’s necessary to retain all data from one or both tables, regardless of whether they match.
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Comparison Chart
Matching Rows
Displays only matching rows from both tables
Shows matching rows plus non-matching rows from one or both tables
Type of Data Displayed
Only rows with corresponding matches in each table
All rows from one or both tables, with NULLs for non-matches
Use Case
Ideal for precise data correlation and integrity
Suitable for comprehensive data analysis, retaining all information
Result on Non-Matching Rows
Excludes non-matching rows
Includes non-matching rows, marked with NULLs
Data Completeness
May result in data loss if no matching rows exist
Ensures no data loss, displaying all rows from joined tables
Compare with Definitions
Inner Join in SQL
Intersects data from different tables, displaying common rows.
The INNER JOIN query provided a list of shared suppliers between two companies.
Outer Join in SQL
Joins tables and includes all rows from one or both tables, filling unmatched rows with NULLs.
SELECT * FROM table1 LEFT OUTER JOIN table2 ON table1.id = table2.id; includes all records from table1.
Inner Join in SQL
Combines related data from joined tables, showing only matches.
The report used an INNER JOIN to combine customer and order data based on customer ID.
Outer Join in SQL
Extends INNER JOIN to include non-matching rows with NULLs in relevant columns.
A LEFT OUTER JOIN was used to list all employees, with details of their projects where applicable.
Inner Join in SQL
Merges rows from multiple tables where join conditions are met.
SELECT * FROM table1 INNER JOIN table2 ON table1.id = table2.id; retrieves matched records from both tables.
Outer Join in SQL
Provides a comprehensive data set from joined tables, including discrepancies.
The OUTER JOIN highlighted the employees not assigned to any project.
Inner Join in SQL
A SQL join that filters out rows without corresponding matches.
Using an INNER JOIN ensured only students enrolled in both courses were listed.
Outer Join in SQL
Merges rows from joined tables, ensuring no data is excluded.
The FULL OUTER JOIN displayed all products and their orders, including those without orders.
Inner Join in SQL
Connects tables based on a related column, excluding unmatched rows.
The INNER JOIN helped identify employees who worked on multiple projects.
Outer Join in SQL
A SQL join type that encompasses unmatched rows in the result.
Using a RIGHT OUTER JOIN, we obtained all vendors, including those with no associated contracts.
Common Curiosities
When should I use an Inner Join?
When you need to combine data from multiple tables but only display rows that have matching data in both tables.
What is an Outer Join in SQL?
Joins tables and shows all rows from one or both tables, filling in NULLs where there are no matches.
How does an Inner Join differ from a Full Outer Join?
Inner Join shows only matching rows, while Full Outer Join includes all rows from both tables, with NULLs for non-matches.
Are Outer Joins necessary for comprehensive data analysis?
Yes, they are crucial when you need to ensure no data is excluded from either table.
How do Outer Joins handle unmatched rows?
They include unmatched rows, filling in NULLs for missing data.
What are the types of Outer Joins?
Left Outer Join, Right Outer Join, and Full Outer Join.
Do Inner Joins improve query performance?
Often, because they return a smaller, more relevant data set.
What is an Inner Join in SQL?
Joins tables based on a related column, showing only rows that have matches in both tables.
Can Outer Joins result in NULL values?
Yes, Outer Joins include NULLs for columns in rows that don’t have a match in the other table.
Is Inner Join the default join type in SQL?
Yes, when JOIN is used without specifying the type, it defaults to Inner Join.
Can I use multiple Inner Joins in a single query?
Yes, you can join several tables using multiple Inner Joins.
What's a key difference in syntax between Inner and Outer Joins?
Outer Joins require specifying 'LEFT', 'RIGHT', or 'FULL', while Inner Join does not.
Which join is better for data integrity checks?
Inner Join, as it strictly shows rows with matches across tables, is better for data integrity checks.
Can I combine Inner and Outer Joins in one query?
Yes, you can mix join types depending on your data retrieval needs.
What happens if there are no matching rows in an Inner Join?
The result set will be empty since Inner Join only displays rows that match in both tables.
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Written by
Tayyaba RehmanTayyaba Rehman is a distinguished writer, currently serving as a primary contributor to askdifference.com. As a researcher in semantics and etymology, Tayyaba's passion for the complexity of languages and their distinctions has found a perfect home on the platform. Tayyaba delves into the intricacies of language, distinguishing between commonly confused words and phrases, thereby providing clarity for readers worldwide.
Co-written by
Urooj ArifUrooj is a skilled content writer at Ask Difference, known for her exceptional ability to simplify complex topics into engaging and informative content. With a passion for research and a flair for clear, concise writing, she consistently delivers articles that resonate with our diverse audience.
