How can I update two different tables in one query? - mysql

Question

I have two tables like this:
// users
+----+--------+----------------------------+------------------+
| id | name | email | notification_num |
+----+--------+----------------------------+------------------+
| 1 | John | John134#gmail.com | 4 |
| 2 | Peter | matrix_peter#ymail.com | 2 |
| 3 | Jack | jk_43m#gmail.com | 6 |
+----+--------+----------------------------+------------------+
// notifications
+----+---------+---------+------+
| id | post_id | user_id | seen |
+----+---------+---------+------+
| 1 | 4325 | 2 | NULL |
| 2 | 8765 | 3 | NULL |
| 3 | 5454 | 3 | 1 |
| 4 | 4346 | 2 | NULL |
| 5 | 3243 | 1 | 1 |
| 6 | 3246 | 2 | 1 |
| 7 | 3764 | 3 | 1 |
+----+---------+---------+------+
Ok, All I have is just a user_id. For example :user_id = 2, And then I want this output:
// users
+----+--------+----------------------------+------------------+
| id | name | email | notification_num |
+----+--------+----------------------------+------------------+
| 1 | John | John134#gmail.com | 4 |
| 2 | Peter | matrix_peter#ymail.com | 0 |
| 3 | Jack | jk_43m#gmail.com | 6 |
+----+--------+----------------------------+------------------+
// notifications
+----+---------+---------+------+
| id | post_id | user_id | seen |
+----+---------+---------+------+
| 1 | 4325 | 2 | 1 |
| 2 | 8765 | 3 | NULL |
| 3 | 5454 | 3 | 1 |
| 4 | 4346 | 2 | 1 |
| 5 | 3243 | 1 | 1 |
| 6 | 3246 | 2 | 1 |
| 7 | 3764 | 3 | 1 |
+----+---------+---------+------+
As you see, I want to update users.cotification_num and set it to 0 (for such an user), and I also want to update notifications.seen and set all rows to 1 (for such an user). How can I do that?
I can do that by two different queries like this:
UPDATE users SET notification_num = 0 WHERE id = :user_id
UPDATE notifications SET seen = 1 WHERE seen is NULL and user_id = :user_id
But I want to know how can I do that by one query?

Answer 1

You can use a multiple-table UPDATE:
UPDATE users u LEFT JOIN notifications n ON n.user_id = u.id
SET u.notification_num = 0,
n.seen = 1
WHERE u.id = 2

Answer 2

You can join the tables together to UPDATE both in a single query:
UPDATE users, notifications
SET users.notification_num = 0
, notification.seen = 1
WHERE users.id = notifications.user_id AND
users.id = 2 AND
notifications.seen is NULL
Read here for more information. Another option would be to simply do 2 separate updates within a transaction:
START TRANSACTION;
UPDATE users SET notification_num = 0 WHERE id = 2;
UPDATE notifications SET seen = 1 WHERE user_id = 2 AND notifications.seen is NULL;
COMMIT;

Answer 3

Note that my schema is very slightly different from yours - but it makes very little difference...
DROP TABLE IF EXISTS users;
CREATE TABLE users
(id INT NOT NULL AUTO_INCREMENT PRIMARY KEY
,name VARCHAR(12) NOT NULL
,email VARCHAR(20) NOT NULL
,notification_num INT NOT NULL
);
INSERT INTO users VALUES
(1,'John','John134#gmail.com',4),
(2,'Peter','matrix_peter#ymail.com',2),
(3,'Jack','jk_43m#gmail.com',6);
DROP TABLE IF EXISTS notifications;
CREATE TABLE notifications
(post_id INT NOT NULL
,user_id INT NOT NULL
,seen TINYINT DEFAULT 0
,PRIMARY KEY(post_id,user_id)
);
INSERT INTO notifications VALUES
(4325,2,0),
(8765,3,0),
(5454,3,1),
(4346,2,0),
(3243,1,1),
(3246,2,1),
(3764,3,1);
SELECT * FROM notifications;
+---------+---------+------+
| post_id | user_id | seen |
+---------+---------+------+
| 3243 | 1 | 1 |
| 3246 | 2 | 1 |
| 3764 | 3 | 1 |
| 4325 | 2 | 0 |
| 4346 | 2 | 0 |
| 5454 | 3 | 1 |
| 8765 | 3 | 0 |
+---------+---------+------+
SELECT * FROM users;
+----+-------+----------------------+------------------+
| id | name | email | notification_num |
+----+-------+----------------------+------------------+
| 1 | John | John134#gmail.com | 4 |
| 2 | Peter | matrix_peter#ymail.c | 2 |
| 3 | Jack | jk_43m#gmail.com | 6 |
+----+-------+----------------------+------------------+
UPDATE users u
JOIN notifications n
ON n.user_id = u.id
SET u.notification_num = 0, n.seen = 1
WHERE u.id = 2;
SELECT * FROM users;
+----+-------+----------------------+------------------+
| id | name | email | notification_num |
+----+-------+----------------------+------------------+
| 1 | John | John134#gmail.com | 4 |
| 2 | Peter | matrix_peter#ymail.c | 0 |
| 3 | Jack | jk_43m#gmail.com | 6 |
+----+-------+----------------------+------------------+
SELECT * FROM notifications;
+---------+---------+------+
| post_id | user_id | seen |
+---------+---------+------+
| 3243 | 1 | 1 |
| 3246 | 2 | 1 |
| 3764 | 3 | 1 |
| 4325 | 2 | 1 |
| 4346 | 2 | 1 |
| 5454 | 3 | 1 |
| 8765 | 3 | 0 |
+---------+---------+------+