How to subtract two date formats in mysql _ MySQL

Mysql sets two date formats to subtract. mysql sets two date formats to Subtract:

Original data table data:

Select (atime-btime) sec from data table;

The subtraction result is not a second. pay special attention to it!

Result:

To calculate the time interval (in seconds) between two Datetime types in mysql, you need to convert:
1. there is no problem across days, months, or years
Select (UNIX_TIMESTAMP (atime)-UNIX_TIMESTAMP (btime) sec

From data table;

2. it can only be used in Time type, cross-day, month, or year.
Select (TIME_TO_SEC (atime)-TIME_TO_SEC (btime) sec

From data table;

Select (TIME_TO_SEC (end_time)-TIME_TO_SEC (start_time) sec from task_detail where end_time is not null;

The results are the same;

Modify data:

Update task_detail set end_time = now () where id = 8;

The query result is a negative value. for details, see:

Therefore, when we subtract two dates, we use(TIME_TO_SEC (atime)-TIME_TO_SEC (btime) secThe method is better.