Inner Join in SQL

Last Updated: 22nd June, 2023

Overview

An inner join in SQL is a join that returns only the data that exists in both tables. It takes two tables as input and returns all rows from both tables where the join condition is true. The join condition is usually a comparison operator like "=", "<", or ">". Inner joins are the most common type of join used in SQL queries. They can combine data from multiple tables and filter the results based on certain criteria. Inner joins are usually faster than other types since only the rows meeting the specified criteria are returned.

Introduction to Inner Join

Saranya had been working as a database specialist for two a long time, but she was still battling to ace SQL. She knew the essentials but needed help with more complex queries. One day, she lurched upon a web journal post about Inner Joins and decided to give it a try. Let's offer assistance to her. An inner join may be a join in SQL utilized to combine records from two or more tables in a database. It returns only those records that have matching values in both tables. It is also known as a simple join.

Syntax

SELECT column_name(s)
FROM table1
INNER JOIN table2
ON table1.column_name = table2.column_name;

The syntax of an inner join includes a SELECT statement that specifies the columns to be returned, the name of the first table, the keyword INNER JOIN, the name of the second table, and a comparison operator that specifies how the tables should be joined. The comparison operator will usually be an equals sign, but it can also be a different operator depending on the type of data in the tables. Once the join is specified, the query returns all records from both tables with matching values in the specified columns.

Example

Products

Prices

SELECT ProductName, Price 
FROM Products 
INNER JOIN Prices 
ON Products.ProductID = Prices.ProductID;

In this example, the inner join combines the Products and Prices tables based on the ProductID column. The query will return all records from both tables with matching values in the ProductID column.

Benefits of Inner Join:

• Inner join is useful for combining data from two or more tables.
• It can be used to filter data, as the result set of an inner join will only include the rows that match the join condition.
• It can be used to join data from multiple tables in a single query.

Limitations of Inner Join:

• Inner join can be computationally intensive as it requires the comparison of every row in one table with every row in another table.
• An inner join can return a large result set, which can cause performance issues.

Alternatives to Inner Join:

• Outer joins (left, right, and full outer joins) can be used to join tables when an inner join is not suitable.
• Subqueries can be used to join tables when an inner join is not suitable.

Common Mistakes with Inner Join:

• Not specifying an ON clause when joining tables.
• Joining tables on a non-related column.
• Joining tables on columns with different data types.
• Not using aliases for table names in a query.

Conclusion

Saranya's knowledge of SQL grew. She began to use Inner Joins in more complex queries and was able to solve problems that she had previously been unable to. Saranya's success with Inner Joins has made her a valuable asset to her company, and she is now the go-to person for all their database-related questions. Thanks to her newfound knowledge, Saranya is now one of the top database specialists in her industry.

Key takeaways

• An inner join in SQL is utilized to combine rows from two or more tables based on a related column between the two tables.
• The inner join is the most common type of join in SQL and is used to retrieve rows from multiple tables based on a common column between them.
• An inner join will only return rows that have a match in both tables.
• An inner join can join multiple tables to create a more complex query.
• When using an inner join, defining the join condition in the WHERE clause is important.
• The order of the tables in the join statement is important and can affect the query results.

Quiz

1. What type of join is used to combine columns from two or more tables in a database?  
   1. Inner Join  
   2. Outer Join  
   3. Self Join 
   4. Cross Join

Answer: A. Inner Join

2. What type of join does an inner join use to combine columns from two or more tables in a database? 
   1. Primary Keys 
   2. Unique Keys 
   3. Foreign Keys 
   4. All of the above

Answer: D. All of the Above

3. What is the syntax used to create an inner join between two tables in SQL? 
   1. SELECT * FROM Table1 INNER JOIN Table2 
   2. SELECT * FROM Table1 JOIN Table2 
   3. SELECT * FROM Table1 WHERE Table2  
   4. SELECT * FROM Table1 ON Table2

Answer: A. SELECT * FROM Table1 INNER JOIN Table2

4. What type of join will return only the rows that have matching values in both tables? 
   1. Inner Join 
   2. Outer Join 
   3. Self Join 
   4. Cross Join

Answer: A. Inner Join