What are the different types of joins in MYSQL?

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In MySQL, joins are used to combine rows from two or more tables based on a related column between them. There are several types of joins in MySQL:

  1. INNER JOIN: An INNER JOIN retrieves rows from both tables that have matching values in the specified columns. If a row in one table does not have a corresponding match in the other table, that row will not appear in the result set.

    sql code
    SELECT*FROM table1 INNERJOIN table2 ON table1.column = table2.column;

  2. LEFT JOIN (or LEFT OUTER JOIN): A LEFT JOIN retrieves all rows from the left table and the matched rows from the right table. If there is no match, NULL values are returned for columns from the right table.

    sql code
    SELECT*FROM table1 LEFTJOIN table2 ON table1.column = table2.column;

  3. RIGHT JOIN (or RIGHT OUTER JOIN): A RIGHT JOIN is the opposite of a LEFT JOIN. It retrieves all rows from the right table and the matched rows from the left table. If there is no match, NULL values are returned for columns from the left table.

    sql code
    SELECT*FROM table1 RIGHTJOIN table2 ON table1.column = table2.column;

  4. FULL JOIN (or FULL OUTER JOIN): A FULL JOIN retrieves rows when there is a match in one of the tables. It returns all rows from both tables and fills in NULL values for columns that do not have a match.

    sql code
    SELECT*FROM table1 FULLJOIN table2 ON table1.column = table2.column;

  5. CROSS JOIN: A CROSS JOIN produces the Cartesian product of two tables, meaning it combines each row from the first table with every row from the second table. It results in a large number of rows and should be used with caution.

    sql code
    SELECT*FROM table1 CROSSJOIN table2;

These are the basic types of joins in MySQL. When working with complex queries involving multiple tables, understanding how to use these join types effectively is crucial.

Examples of JOINS

let's consider two tables: users and orders. The users table contains information about users, and the orders table contains information about orders made by these users. Here's how you might use different types of joins with these tables:

Users Table:

sql code

CREATE TABLE users (

    id INT PRIMARY KEY,

    name VARCHAR(255)

);

INSERT INTO users (id, name)

VALUES (1, 'Alice'),

       (2, 'Bob'),

       (3, 'Charlie');

  Orders Table:

sql code

CREATE TABLE orders (

    id INT PRIMARY KEY,

    user_id INT,

    product_name VARCHAR(255)

);

INSERT INTO orders (id, user_id, product_name)

VALUES (101, 1, 'Product A'),

       (102, 1, 'Product B'),

       (103, 2, 'Product C');    

INNER JOIN:

An INNER JOIN retrieves the rows that have matching values in both tables.

sql code

SELECT users.name, orders.product_name

FROM users

INNER JOIN orders ON users.id = orders.user_id;

Result:

| name   | product_name |

|--------|--------------|

| Alice  | Product A    |

| Alice  | Product B    |

| Bob    | Product C    |

LEFT JOIN:

A LEFT JOIN retrieves all rows from the left table (users) and the matched rows from the right table (orders).

sql code

SELECT users.name, orders.product_name

FROM users

LEFT JOIN orders ON users.id = orders.user_id;

Result:

| name    | product_name |

|---------|--------------|

| Alice   | Product A    |

| Alice   | Product B    |

| Bob     | Product C    |

| Charlie | NULL         |

RIGHT JOIN:

A RIGHT JOIN retrieves all rows from the right table (orders) and the matched rows from the left table (users).

sql code

SELECT users.name, orders.product_name

FROM users

RIGHT JOIN orders ON users.id = orders.user_id;

Result:

| name   | product_name |

|--------|--------------|

| Alice  | Product A    |

| Alice  | Product B    |

| Bob    | Product C    |

| NULL   | NULL         |

FULL JOIN:

MySQL does not support FULL JOIN directly. You can achieve a FULL JOIN using a combination of LEFT JOIN and UNION:

sql code

SELECT users.name, orders.product_name

FROM users

LEFT JOIN orders ON users.id = orders.user_id

UNION

SELECT users.name, orders.product_name

FROM users

RIGHT JOIN orders ON users.id = orders.user_id;

Result:

| name    | product_name |

|---------|--------------|

| Alice   | Product A    |

| Alice   | Product B    |

| Bob     | Product C    |

| Charlie | NULL         |

| NULL    | NULL         |

CROSS JOIN:

A CROSS JOIN produces the Cartesian product of the two tables.

sql code

SELECT users.name, orders.product_name

FROM users

CROSS JOIN orders;

Result:

| name   | product_name |

|--------|--------------|

| Alice  | Product A    |

| Alice  | Product B    |

| Alice  | Product C    |

| Bob    | Product A    |

| Bob    | Product B    |

| Bob    | Product C    |

| Charlie| Product A    |

| Charlie| Product B    |

| Charlie| Product C    |

These examples should give you a clear understanding of how different types of joins work in MySQL.

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