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How To Nail Your Next Tech Interview

Inner Join vs. Outer Join: Exploring SQL Table Relationships
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Inner Join vs. Outer Join: Exploring SQL Table Relationships

Navigating relational databases, have you faced problems in presenting all the information at once? This generally occurs due to information present in distinct tables. Despite their interrelated nature, the intricate web of data can be efficiently explored through the strategic application of join operators. These operators not only tend to execute faster but also mitigate the processing burden. However, having in-depth information of inner join vs. outer join is important to perform tasks in a relational database. Explore how SQL table relationships can be used to get the desired result. 

Here is what we’ll cover in this article:

Understanding Join in SQL

Join in SQL aid in retrieving information from multiple tables that share the same field. It means one can easily combine data from two or more tables of any database that possesses common or relational information. The join operator aids in getting consolidated outcomes from diverse tables with single join queries rather than multiple queries. Joins are commonly divided into two types, i.e., inner join and outer join. 

What is Inner Join?

Inner join, also called simple join, enables data to be fetched from two tables with the common column. Inner join in SQL returns the matching data from the database based on certain specifications. The data is combined from two tables linked with a common column. The specification is expressed using the ON keyword in SQL. The rows that fulfill the join condition from two or more tables are retrieved in the outcome, especially. If a row from one table does not have a matching row in the second table, it will be excluded from the inner join result.

Inner Join
Scaler

Advantages and Disadvantages of Inner Join

Let us discover how Inner Join benefits us and what challenges we may face using the same.

Advantages

Effective Query Execution: When compared to outer joins, inner joins tend to be more efficient when it comes to query execution time since inner joins  retrieve only the rows with matching values.

Data Accuracy: As only matching information is delivered in the outcome, it ensures the data does not hold any mismatched value or irrelevant information. Thus, the inner join ensures data accuracy.

Limits Data Repetition: Inner join returns only the rows with matching information from the linked or joined tables, reducing the amount of duplicate information in the outcome.

Disadvantages 

Complexity in Query: The difficulty and complexity increases with an increase in tables. Thus, inner joins become hard to write and understand while handling multiple tables.

Loss of Data: As the inner join only reverts matching information in the linked tables, if there are no matching values, the other information can be lost.

Overlapping Data: In certain conditions, inner joins may also return overlapping data, requiring additional processing for accuracy in the outcome.

What is Outer Join?

In the outer join, all the rows of one table and the matching values from the second table are retrieved on certain specifications. It means the outcome holds information on rows from one table that does not possess any matching values in the rows of the linked table. The combined data is received from the linked columns between the tables through the ON keyword in SQL. Outer join is categorized in three forms:

  1. Left Outer Join

Here, the outcome returns all the values from the left table and only the matching values from the right table rows. In case the left table does not possess any matching information in the right table rows, the outcome portrays the null values for the right table columns.

 Left Outer Join
Dofactory

  1. Right Outer Join

It is similar to the left outer join but replacing it with the ‘left.’ Here, the outcome retrieved holds all the rows of the right table and only the matching information of the rows of the left table. In case the right table rows do not hold any matching information or value in the rows of the left table, it will be portrayed as a null value for the left table columns.

Right Outer Join
Dofactory

  1. Full Outer Join

It returns the results of both the left and right outer join. Here, the results possess all the rows of both the tables, i.e., matching and non-matching. In case a row of one table does not hold a matching value in the row of the second table, it will be portrayed as a null value for the column that has no match. 

Full Outer Join
Dofactory

Advantages and Disadvantages of Outer Join

Let us explore how outer join benefits us and the challenges we may face while working with the same.

Advantages

Integrity in Data: Data integrity is maintained in the outer join as all the data from the primary table is retrieved, regardless of matching values in the secondary table.

Analysis of Data: It is the best fit for analyzing relationships between tables in a database. In addition, the link created by the outer join between the datasets aids in finding the patterns and the trends.

Enhanced Data Retrieval: The result set includes more data, both matching and non-matching rows, when compared to the inner join. It is because the outer join displays non-matching rows as well.

Disadvantages

Repetition of Data: In case the secondary table possesses multiple matching information or values, the outer join produces duplicate data.

Slow Query Execution: Outer join tends to be slower in performing tasks, especially when dealing with big data. 

Quality of Data: When the linked tables hold incomplete or inconsistent data, the outer join will also deliver inaccurate or incomplete data.

Gear Up for the Next Opportunity with Interview Kickstart

A solid understanding of SQL is imperative, particularly in key concepts such as inner join vs. outer join. Once equipped with the requisite skills, the challenge shifts to interview preparation. 

Having trained 17000+ candidates, Interview Kickstart specializes in comprehensive training for all those aiming to secure positions in FAANG+ companies. Our seasoned professionals provide targeted guidance, ensuring you are well-prepared to excel in your interviews and land your dream job. What are you waiting for? Join our webinar today for free!

FAQs

Q1. How do you know when to use outer join vs. inner join?

It depends on your requirements. If you need only matching values from the paired tables, you can pick the inner join in SQL. However, if you need both matching and non-matching values, you must use outer join in SQL.

Q2. When should I use left outer join vs. inner join SQL?

If you require all the values from the left table, you can go for the left outer join. It does not matter whether the left table is linked with the right table or not. However, the inner join only retrieves matching data from both sides of the tables.

Q3. Which is faster in inner join vs. left outer join?

An outer join tends to be faster in comparison to an inner join. In outer join, left outer joins are faster than others. However, outer joins can get slower when dealing with multiple tables.

Q4. Do outer joins cause duplicates?

Outer joins may provide duplicate values as the records are retrieved from both tables, whereas the secondary table may have multiple matching information.

Q5. Does Inner Join provide specific values?

Inner join retrieves only matching data from two or more tables. Thus, the values are accurate and specific. 

Q6. Can I prevent duplicates in the inner join?

You can add a filter to the data after linking tables and use primary key columns in the join while performing an inner join with multiple matching records.

Last updated on: 
February 13, 2024
Author

Ashmita Roy

Senior Content Specialist at Interview Kickstart

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Inner Join vs. Outer Join: Exploring SQL Table Relationships

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