http://www.valentina-db.com/bt/view.php?id=8600

Seems to be a bug.

You may use following as a workaround:

set @val_seconds = select datediff( '08/14/2019 01:30:00', '08/13/2019 20:30:00', 'second');

select sec_to_time( @val_seconds);

Ok, try this:

select datediff( '08/14/2019 01:30:00', '08/13/2019 20:30:00', 'second')
result: 18000
Now put that into sec_to_time
select sec_to_time (datediff( '08/14/2019 01:30:00', '08/13/2019 20:30:00', 'second'))
result: <NULL>

select datediff( '08/13/2019 00:00:00', '07/13/2019 00:00:00', 'second')

-- 2678400 

It is correct. But how "month" could be represented as a time_value? It must be a DateTime.

select dateadd( '07/13/2019 00:00:00', 'second', 2678400 )

-- '08/13/2019 00:00:00'

But why does: datediff(Time_end, Time_start, 'second')as seconds shows the right number then ?

isn't it the same... but with one added expression ?

or is it that the sec_to_time, needs a number and not a string...

is there a command for converting string to number. like VAL(string) ?

It seems that seconds could not be represented as a Time_value because there is a date part also.

Full date and time. Inputted in studio for the test.

Seems to be a bug. What the values in Time_end and Time_start?