MySQL更新字段与来自同一表中另一个字段的值

Question

I have a table like this:

----------------------------------
| id | date1      | date2 | type |
----------------------------------
| 1  | NULL       | NULL  | A    |
| 1  | NULL       | NULL  | B    |
| 1  | NULL       | NULL  | A    |
| 1  | NULL       | NULL  | A    |
| 1  | 2016-08-02 | NULL  | C    |
| 1  | NULL       | NULL  | B    |
| 2  | NULL       | NULL  | A    |
| 2  | NULL       | NULL  | A    |
| 2  | NULL       | NULL  | A    |
| 2  | NULL       | NULL  | B    |
| 2  | 2016-08-15 | NULL  | C    |
| 2  | NULL       | NULL  | B    |
----------------------------------

and I would like that become by single query like this:

----------------------------------------
| id | date1      | date2       | type |
----------------------------------------
| 1  | NULL       | 2016-08-02  | A    |
| 1  | NULL       | 2016-08-02  | B    |
| 1  | NULL       | 2016-08-02  | A    |
| 1  | NULL       | 2016-08-02  | A    |
| 1  | 2016-08-02 | NULL        | C    |
| 1  | NULL       | 2016-08-02  | B    |
| 2  | NULL       | 2016-08-15  | A    |
| 2  | NULL       | 2016-08-15  | A    |
| 2  | NULL       | 2016-08-15  | A    |
| 2  | NULL       | 2016-08-15  | B    |
| 2  | 2016-08-15 | NULL        | C    |
| 2  | NULL       | 2016-08-15  | B    |
----------------------------------------

The date to get will be always "type C" and the field to update will be always the same id of the date and "type A" or "type B"

Any suggest?

Answer 1

You could use an updated joined on subselect

 update my_table 
 inner join  ( select id, date1 from my_table where type ='C') t2
 on my_table.id = t2.id
 set date2 = t2.date1
 where type in ('A','B')

Answer 2

UPDATE myTable t1
SET date2 = (SELECT MAX(date1)
             FROM myTable t2 
             WHERE t2.id = t1.id)
WHERE t1.type <> 'C'