Join Two or More Tables
You can combine rows from two or more tables, based on a related column between them, by using a JOIN statement.
Consider you have a “users” table and a “products” table:
users
{ id: 1, name: ‘John’, fav: 154},
{ id: 2, name: ‘Peter’, fav: 154},
{ id: 3, name: ‘Amy’, fav: 155},
{ id: 4, name: ‘Hannah’, fav:},
{ id: 5, name: ‘Michael’, fav:}
products
{ id: 154, name: ‘Chocolate Heaven’ },
{ id: 155, name: ‘Tasty Lemons’ },
{ id: 156, name: ‘Vanilla Dreams’ }
These two tables can be combined by using users’ fav field and products’ id field.
Example
Join users and products to see the name of the users favorite product:
import mysql.connector
mydb = mysql.connector.connect(
host=”localhost”,
user=”yourusername“,
password=”yourpassword“,
database=”mydatabase”
)
mycursor = mydb.cursor()
sql = “SELECT \
users.name AS user, \
products.name AS favorite \
FROM users \
INNER JOIN products ON users.fav = products.id”
mycursor.execute(sql)
myresult = mycursor.fetchall()
for x in myresult:
print(x)
Output:
C:\Users\My Name>python demo_mysql_inner_join.py
(‘John’, ‘Chocolate Heaven’)
(‘Peter’, ‘Chocolate Heaven’)
(‘Amy’, ‘Tasty Lemon’)
Note: You can use JOIN instead of INNER JOIN. They will both give you the same result.
LEFT JOIN
In the example above, Hannah, and Michael were excluded from the result, that is because INNER JOIN only shows the records where there is a match.
If you want to show all users, even if they do not have a favorite product, use the LEFT JOIN statement:
Example
Select all users and their favorite product:
sql = “SELECT \
users.name AS user, \
products.name AS favorite \
FROM users \
LEFT JOIN products ON users.fav = products.id”
Output:
C:\Users\My Name>python demo_mysql_left_join.py
(‘John’, ‘Chocolate Heaven’)
(‘Peter’, ‘Chocolate Heaven’)
(‘Amy’, ‘Tasty Lemon’)
(‘Hannah’, None)
(‘Michael’, None)
RIGHT JOIN
If you want to return all products, and the users who have them as their favorite, even if no user have them as their favorite, use the RIGHT JOIN statement:
Example
Select all products, and the user(s) who have them as their favorite:
sql = “SELECT \
users.name AS user, \
products.name AS favorite \
FROM users \
RIGHT JOIN products ON users.fav = products.id”
Output:
C:\Users\My Name>python demo_mysql_right_join.py
(‘John’, ‘Chocolate Heaven’)
(‘Peter’, ‘Chocolate Heaven’)
(‘Amy’, ‘Tasty Lemon’)
(None, ‘Vanilla Dreams’)
Note: Hannah and Michael, who have no favorite product, are not included in the result.