mysql - 合并 MySQL 列排除重复项

Question

我有这两张表:

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       |                |
+-----------------------+---------+------+-----+---------+----------------+

我想将 students.student_ticket_number 列 move 到 studentdates.student_ticket_number 字段 student_id 匹配的地方。

因此，如果用户 John 的 student_id = 1，则将他的票号(例如 1234)从 students.student_ticket_number move 到 studentdates.student_ticket_number WHERE student_id = '1 '.

在表 studentdates.student_id 中可以有多个相同的记录，那么我想使用最低的 studentdates.student_date_id 并跳过其他记录。如果不清楚，请告诉我。

我想我需要以某种方式进行子查询，但是怎么做呢？

Answer 1

您需要获得最小值 student_date_ID在子查询中，然后将其与其他表连接起来。试试这个，

<罢工>

<罢工>

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'

<罢工>

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'