How to update one table based on another one?

Question

I have these two tables:

// user
+----+-------+------------+
| id |  name | total_rep  |
+----+-------+------------+
| 1  | Jack  | 100        |
| 2  | Peter | 334        |
| 3  | John  | 1          |
| 4  | Ali   | 5463       |
+----+-------+------------+

// rep
+----+------------+---------+------+
| id | reputation | id_user | done |
+----+------------+---------+------+
| 1  | 5          | 2       | 1    |
| 2  | 2          | 3       | 1    |
| 3  | 15         | 2       | Null |
| 4  | 10         | 2       | Null |
| 5  | 5          | 4       | 1    |
| 6  | 10         | 3       | Null |
+----+------------+---------+------+

I'm trying to sum the number of reputation column from rep table where done is Null for specific user and then add it to total_rep column from user table. So it is expected output:

// specific user
$id = 2;

// user
+----+-------+------------+
| id |  name | total_rep  |
+----+-------+------------+
| 1  | Jack  | 100        |
| 2  | Peter | 359        | -- this is updated
| 3  | John  | 1          |
| 4  | Ali   | 5463       |
+----+-------+------------+

Note: Then I will update done column and set all Null values for that user to 1 . (this is not my question, I can do that myself)

How can I do that?

Answer 1

One way to do it is to use the result of a subquery as a scalar value in an update statement.

UPDATE `user` 
SET total_rep = total_rep + (
    SELECT SUM(reputation) AS rep_sum FROM `rep` WHERE done IS NULL AND id_user = 2)
WHERE id = 2;

Answer 2

You can't update two tables in one statement, so you will need to execute a transaction. Or maybe in some code do the next thing I'll make it in PHP

$query_result=DB::select('Select sum(reputation) as reputation, id_user from rep where done is null group by id_user');

foreach($query_result as $result){
    //update the data
}

You have to take the data and update firstable the reputation table to clean it and then the user table to sum the rep values