DML: SELECT with INNER JOIN

The INNER JOIN keyword in SQL combines records from two or more tables based on a related column. The INNER JOIN keyword selects records that have matching values in both tables.

Syntax

SELECT column_name(s)
FROM table_1
INNER JOIN table_2
ON table_1.column_name = table_2.column_name;

• table_1: First table.
• table_2: Second table.
• column_name(s): The name(s) of the column(s) to be retrieved from the table(s).
• table_1.column_name = table_2.column_name: The common field between the two tables.

Simple Example

Consider the following two tables,

Table: student

Table: grade

Here, the id column in both tables is the common field. An INNER JOIN of these two tables could look like this:

SELECT student.name, grade.subject, grade.grade
FROM student
INNER JOIN grade
ON student.id = grade.id;

This would output:

As you can see, each row in the student table is combined with each row from the grade table with a matching id.

Complex Example

INNER JOIN can be used to join more than two tables. Let’s add another table to the mix.

Table: subject

Now, we can join all these tables as shown:

SELECT student.name, subject.name, grade.grade
FROM ((student
INNER JOIN grade ON student.id = grade.id)
INNER JOIN subject ON grade.subject = subject.id);

This would output:

Further Readings

• SQL INNER JOIN Keyword - W3Schools
• Understanding SQL Joins - MySQLTutorial