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MySQL JOIN


MySQL JOINS are used with SELECT statement. It is used to retrieve data from multiple tables. It is performed whenever you need to fetch records from two or more tables.

There are three types of MySQL joins:

  • MySQL INNER JOIN (or sometimes called simple join)
  • MySQL LEFT OUTER JOIN (or sometimes called LEFT JOIN)
  • MySQL RIGHT OUTER JOIN (or sometimes called RIGHT JOIN)

MySQL Inner JOIN (Simple Join)

The MySQL INNER JOIN is used to return all rows from multiple tables where the join condition is satisfied. It is the most common type of join.

Syntax:

  1. SELECT columns
  2. FROM table1
  3. INNER JOIN table2
  4. ON table1.column = table2.column;

Image representation:

image1

Let’s take an example:

Consider two tables “officers” and “students”, having the following data.

image2

Execute the following query:

  1. SELECT officers.officer_name, officers.address, students.course_name
  2. FROM officers
  3. INNER JOIN students
  4. ON officers.officer_id = students.student_id;

Output:

image3

MySQL Left Outer Join

The LEFT OUTER JOIN returns all rows from the left hand table specified in the ON condition and only those rows from the other table where the join condition is fulfilled.

Syntax:

  1. SELECT columns
  2. FROM table1
  3. LEFT [OUTERJOIN table2
  4. ON table1.column = table2.column;

Image representation:

image4

Let’s take an example:

Consider two tables “officers” and “students”, having the following data.

image5

Execute the following query:

  1. SELECT  officers.officer_name, officers.address, students.course_name
  2. FROM officers
  3. LEFT JOIN students
  4. ON officers.officer_id = students.student_id;

Output:

image6

MySQL Right Outer Join

The MySQL Right Outer Join returns all rows from the RIGHT-hand table specified in the ON condition and only those rows from the other table where he join condition is fulfilled.

Syntax:

  1. SELECT columns
  2. FROM table1
  3. RIGHT [OUTERJOIN table2
  4. ON table1.column = table2.column;

Image representation:

image7

Let’s take an example:

Consider two tables “officers” and “students”, having the following data.

image8

Execute the following query:

  1. SELECT officers.officer_name, officers.address, students.course_name, students.student_name
  2. FROM officers
  3. RIGHT JOIN students
  4. ON officers.officer_id = students.student_id;

Output:

image9

 

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