ansi SQL date function in Oracle - sql

Question

I realize I could use a combination of to_char and to_date and what not as a work-around, but I'm trying to figure out why this doesn't work. I am using Oracle 12.1
select '2016-10-01'
from dual
union all
select to_char(2016)||'-10-01'
from dual;
Each side of the union produces identical output: 2016-10-01. If I then try to use the ANSI date syntax (as described here: http://blog.tanelpoder.com/2012/12/29/a-tip-for-lazy-oracle-users-type-less-with-ansi-date-and-timestamp-sql-syntax/ ), it only works on the first one, not the second one:
select date '2016-10-01'
from dual
This returns: 10/1/2016
But if I try this:
select date to_char(2016)||'-10-01'
from dual;
I get on:
ORA_00936 missing expression error.
I can code a work-around, but I'm stumped as to why one works and the other does not.

Answer 1

It won't work that way because DATE is not a function but a literal.
The terms literal and constant value are synonymous and refer to a fixed data value.
Date Literals
You can specify a DATE value as a string literal, or you can convert a character or numeric value to a date value with the TO_DATE function. DATE literals are the only case in which Oracle Database accepts a TO_DATE expression in place of a string literal.
You could use TO_DATE function.
select TO_DATE(to_char(2016)||'-10-01', 'YYYY-MM-DD')
from dual;
Rextester Demo
EDIT:
Using dynamic-SQL:
DECLARE
i DATE;
stmt VARCHAR2(100);
BEGIN
stmt := q'{SELECT DATE '}' || TO_CHAR(2016) || '-01-01' || q'{' FROM dual}';
EXECUTE IMMEDIATE stmt INTO i;
DBMS_OUTPUT.PUT_LINE('i =>' || i);
END;