mysql update multiple columns with same now()

Solution 1:

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;

Solution 2:

Mysql isn't very clever. When you want to use the same timestamp in multiple update or insert queries, you need to declare a variable.

When you use the now() function, the system will call the current timestamp every time you call it in another query.

Solution 3:

MySQL evaluates now() once per statement when the statement commences execution. So it is safe to have multiple visible now() calls per statement.

select now(); select now(), sleep(10), now(); select now();
+---------------------+
| now()               |
+---------------------+
| 2018-11-05 16:54:00 |
+---------------------+
1 row in set (0.00 sec)

+---------------------+-----------+---------------------+
| now()               | sleep(10) | now()               |
+---------------------+-----------+---------------------+
| 2018-11-05 16:54:00 |         0 | 2018-11-05 16:54:00 |
+---------------------+-----------+---------------------+
1 row in set (10.00 sec)

+---------------------+
| now()               |
+---------------------+
| 2018-11-05 16:54:10 |
+---------------------+
1 row in set (0.00 sec)