SQL JOIN

A INNER JOIN keyword selects records that have matching values in both tables.

Let's look at a selection from the "products" table:

product table inner join

Then look at a selection from the "employee" table:

category table

We will join the Products table with the Categories table, by using the CategoryID field from both tables:

Example

Join Products and Categories with the INNER JOIN keyword:
              
 SELECT  Product_id, Product_name, Category_name
 FROM  products
 INNER JOIN category  ON  products.Category_id = category.Category_id;

You can click on above box to edit the code and run again.

Output

Note:The INNER JOIN keyword returns only rows with a match in both tables. Which means that if you have a product with no Category_id, or with a Category_id that is not present in the Category table, that record would not be returned in the result.

Syntax

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

Naming the Columns

It is a good practice to include the table name when specifying columns in the SQL statement.

Example

SELECT  products . Product_id , products . Product_name , category . Category_name
 FROM  products
 INNER JOIN category  ON  products.Category_id = category.Category_id;

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Output

The example above works without specifying table names, because none of the specified column names are present in both tables. If you try to include Category_id in the SELECT statement, you will get an error if you do not specify the table name (because Category_id is present in both tables).

JOIN or INNER JOIN

JOIN and INNER JOIN will return the same result.

INNER is the default join type for JOIN , so when you write JOIN the parser actually writes INNER JOIN

JOIN Three Tables

The following SQL statement selects all products with employee and category information:

Example

SELECT  products . Product_id , employee . Employee_name , category . Category_name
 FROM (( products
 INNER JOIN employee  ON  products.Employee_id = employee.Employee_id)
   INNER JOIN category  ON  products.Category_id = category.Category_id);

You can click on above box to edit the code and run again.