When casting a datetime as date, why does SQLite3 only return the year and not the full date? - sqlite

Question

I know that you can cast a datetime to date using the date() function:
sqlite> select date('2000-01-01 10:00:00');
2000-01-01
But why does SQLite3's cast expression such as in
sqlite> select cast('2000-01-01 10:00:00' as date);
2000
only return the year?
Even using an explicit datetime() setup solely returns the year:
sqlite> select cast(datetime('2000-01-01 10:00:00') as date);
2000
Or:
sqlite> select cast(datetime('now') as date);
2019
Looking at Postgresql, it resolves both properly:
postgresql> select date('2000-01-01 10:00:00');
2000-01-01
postgresql> select cast('2000-01-01 10:00:00' as date);
2000-01-01
What's the technical explanation for SQLite3's – to me unexpected – behavior?

Answer 1

For SQLite there is no Date datatype. As mentioned in their documentation here: https://www.sqlite.org/datatype3.html
What you use as Date is actually TEXT.
You can check that:
select typeof(datetime('now'));
returns:
text
And:
select typeof(cast(datetime('now') as date));
returns:
integer
So the result of cast('2000-01-01 10:00:00' as date) is an integer and it's the same
integer that you get by:
select '2000-01-01 10:00:00' + 0
when SQLite implicitly converts '2000-01-01 10:00:00' to 2000 in order to use it in a mathematical operation.
In the case of dates it happens to be the numeric value of the year, but in general SQLite returns the longest substring of the TEXT, starting from the 1st character, that can be represented as an integer.
So for '2000-01-01 10:00:00' it's the substring until the 1st -, which is the year.