Radu Maris Radu Maris - 1 month ago 23
MySQL Question

mysql update multiple columns

I need to update 2 datetime columns, and I need them to be exactly the same, using mysql version 4.1.20. I'm using this query:

mysql> update table set last_update=now(), last_monitor=now() where id=1;


It is safe or there is a chance that the columns are update with different time, beacause of the 2 visible calls to now() ?

I don't think that it can be update with different values (I think internaly mysql calls now() just once per row or something similar) , but I'm not an expert, what do you think ?

Second question why this query doesn't update the columns:

mysql> update table set last_update=last_monitor=now() where id=1;
Query OK, 0 rows affected (0.00 sec)
Rows matched: 1 Changed: 0 Warnings: 0


Thank you.

Answer

Found a solution:

mysql> UPDATE table SET last_update=now(), last_monitor=last_update WHERE id=1;

I found this in MySQL Docs and after a few tests it works:

the following statement sets col2 to the current (updated) col1 value, not the original col1 value. The result is that col1 and col2 have the same value. This behavior differs from standard SQL.

UPDATE t1 SET col1 = col1 + 1, col2 = col1;

On the second question, don't have any answers, did find nothing on mysql docs about this.