Merge MySQL columns exclude duplicates

Question

I have these two tables:

desc students
+-----------------------+---------+------+-----+---------+----------------+
| Field                 | Type    | Null | Key | Default | Extra          |
+-----------------------+---------+------+-----+---------+----------------+
| student_id            | int(11) | NO   | PRI | NULL    | auto_increment |
| student_ticket_number | int(11) | YES  |     | 0       |                |
+-----------------------+---------+------+-----+---------+----------------+

desc studentdates
+-----------------------+---------+------+-----+---------+----------------+
| Field                 | Type    | Null | Key | Default | Extra          |
+-----------------------+---------+------+-----+---------+----------------+
| student_date_id       | int(11) | NO   | PRI | NULL    | auto_increment |
| student_id            | int(11) | YES  |     | NULL    |                |
| student_ticket_number | int(11) | YES  |     | 0       |                |
+-----------------------+---------+------+-----+---------+----------------+

I would like to move the column students.student_ticket_number to studentdates.student_ticket_number where the field student_id match.

So if the user John has student_id = 1 move his ticketnumber (for example 1234) from students.student_ticket_number to studentdates.student_ticket_number WHERE student_id = '1'.

In the table studentdates.student_id there can be multiple identical records then I would like to use the lowest studentdates.student_date_id and skip the others. Tell me if this is unclear.

I guess I need to do a subquery somehow but how?

Answer 1

You need to get the minimum student_date_ID in a subquery then join it with the other tables. try this,

UPDATE  students a
        INNER JOIN studentdates b
            ON a.student_ID = b.student_ID
        INNER JOIN
        (
            SELECT  student_ID, MIN(student_date_ID) minID
            FROM    studentDates
            GROUP BY student_ID
        ) c ON b.student_ID = c.student_ID AND
               b.student_date_id = c.minID
SET     a.student_ticket_number = b.student_ticket_number
WHERE   a.student_id = '1'

UPDATE  students a
        INNER JOIN studentdates b
            ON a.student_ID = b.student_ID
        INNER JOIN
        (
            SELECT  student_ID, MIN(student_date_ID) minID
            FROM    studentDates
            GROUP BY student_ID
        ) c ON b.student_ID = c.student_ID AND
               b.student_date_id = c.minID
SET     b.student_ticket_number = a.student_ticket_number
WHERE   a.student_id = '1'