Similar to programming languages, is it possible to create a temporary variable and define it a value? e.g.
String date = '12-MAY-12'
Select COUNT (*) FROM TABLEX WHERE TABLE_DATE < DATE;
The answer is, it depends.
It depends on environment you use.
For example, Allround Automations PL/SQL Developer accepts sign
& before string for variables (values of them are asked during query execution):
SELECT COUNT (*) FROM TABLEX WHERE TABLE_DATE < &DATE;