Convert datetime column to 24 hour format - mysql

Question

I have a column called schedule_time (datetime) format. I want to convert the time to 24 hour time.
2016-03-08 03:00:00 to 2016-03-08 15:00:00

Answer 1

Please note that DATETIME values are always stored in 24h format (http://dev.mysql.com/doc/refman/5.7/en/datetime.html). There is no AM/PM.
When you want to display the values, there is however the DATE_FORMAT
function, which will format the value according to your needs, including AM/PM:
select DATE_FORMAT(schedule_time, '%Y-%m-%d %h:%i:%s %p') from t1;
This will give 2016-03-08 03:00:00 AM and 2016-03-08 03:00:00 PM. But the values in the DB are still the same, in 24h format.
If adding 12 hours would solve your issue, the you can do it like this:
start transaction;
update t1 set schedule_time = date_add(schedule_time, interval 12 hour);
select * from t1; -- verify!!!
rollback;
-- or commit;
I put this in a transaction so you can first verify your results. If they are wrong, simply rollback the transaction (provided you use InnoDB tables). If you don't have transactions (or feel uncomfortable with them), you can undo the change with date_sub instead of date_add.
But be aware: This doesn't change from 12h to 24h format, it simply adds 12 hours to all your schedule_time values.

Answer 2

Use MySQL's DATE_FORMAT function.
The format string will be '%Y-%m-%d %T'.
Selecting the current date with 24-hour time:
mysql> SELECT DATE_FORMAT(NOW(), '%Y-%m-%d %T') AS now
+---------------------+
| now |
+---------------------+
| 2016-03-08 20:47:04 |
+---------------------+
1 row in set (0.00 sec)
Selecting a date with 24-hour time from a table:
mysql> SELECT DATE_FORMAT(`created_at`, '%Y-%m-%d %T') AS created_at FROM test.comments;
+---------------------+
| created_at |
+---------------------+
| 2016-02-25 16:32:12 |
+---------------------+
1 row in set (0.00 sec)