我想更新mysql表column1，除非数据存在，然后移至下一个column2

Question

I want to update my MySQL table. What I want to do is update column1 unless data exists in column1 then move it onto column2 and update that one instead. The code that I currently have is constantly updating the first column.

UPDATE users
SET    active = 1,
       time_started = '$_POST[in_time]'
WHERE  user_id = '$_POST[user_id]

Could anyone help on this?

Answer 1

Something like:

update users set active=1, time_in_1=if(time_started is null,time_in_1,?), time_started=if(time_started is null,?,time_started) while ...

In effect, when time_started is null, the above does:

update users set time_in_1=time_in_1, time_started=?

(leaving time_in_1 unchanged; ? is a placeholder for your new value). If time_started is not null, it does:

update users set time_in_1=?, time_started=time_started

(leaving time_started unchanged). In either case, you need to provide your new value twice (assuming there is only one; maybe you want to update the second column to a different value than you would have updated the first column to?).