Subtracting a date from another date - sql

Question

I am trying to subtract one date from another but having issues:
SELECT MIN(date) AS first_day,
MAX(date) AS last_date,
((MAX(date)) - (MIN(date))) AS totaL_days
FROM dates;
Could someone please clarify the number format of the number it is returning below?
+------------+
| total_days |
+------------+
| 29001900 |
I have tried using DATEDIFF but this rounds the days to the nearest whole number and I need to carry out further calculations with the data. The rounding means my solutions are a little off.
In the version of DB I am using DATEDIFF() only takes two parameters so always has to be days as far as I'm aware, I get an error if I try to use hours.

Answer 1

SELECT DATEDIFF
(
SELECT MAX(date) FROM dates,
SELECT MIN(date) FROM dates
)
AS totaL_days;
should do the trick.

Answer 2

I'm assuming your RDBMS is a MySql.
Then that number you got would be the seconds between those 2 datetimes.
Because if you subtract 2 DATE types you would get the days between them.
There's more than DATEDIFF to work with.
Test data
create table mytest (
id int auto_increment primary key,
date_col date not null,
datetime_col datetime not null
);
insert into mytest(date_col, datetime_col) values
('2021-06-16', '2021-06-16 14:15:30')
,('2021-07-16', '2021-07-16 19:06:15')
Test using dates
select
min(date_col) as min_date
, max(date_col) as max_date
, max(date_col) - min(date_col) as subtracted
, datediff(max(date_col), min(date_col)) as days
from mytest
min_date | max_date | subtracted | days
:--------- | :--------- | ---------: | ---:
2021-06-16 | 2021-07-16 | 100 | 30
Test using datetimes
select
min(datetime_col) as min_date
, max(datetime_col) as max_date
, max(datetime_col) - min(datetime_col) as seconds
, datediff(max(datetime_col), min(datetime_col)) as days
from mytest
min_date | max_date | seconds | days
:------------------ | :------------------ | --------: | ---:
2021-06-16 14:15:30 | 2021-07-16 19:06:15 | 100049085 | 30
Using sec_to_time and extract
select seconds
, sec_to_time(seconds) as tm
, extract(day from sec_to_time(seconds)) as days
from (
select
max(datetime_col) - min(datetime_col) as seconds
from mytest
) q
seconds | tm | days
--------: | :-------- | ---:
100049085 | 838:59:59 | 30
db<>fiddle here