Adding time(hh:mm:ss) to a datetime field in SQL

Question

I want to add the run_duration column(hh:mm:ss) to the run_datetime(datetime) column to calculate the endtime by using the following query:

SELECT checkdate, run_datetime, run_duration,
cast(run_datetime as datetime) + cast(run_duration as datetime) as readytime, 
cast(cast(run_datetime as datetime) + cast(run_duration as datetime) as datetime) as readytime_datetime
FROM table

The problem is that it is not adding up correctly for some records because it is summing above the 60 seconds:

Is there another way to do this correctly?

Answer 1

Use MySQL's built-in addtime() function instead of the + operator:

SELECT checkdate,
       run_datetime,
       run_duration,
       addtime(cast(run_datetime as datetime), cast(run_duration as time)) as readytime
FROM table

The + operator converts the datetimes to numbers and adds them up as such.