interval function in oracle

Question

Query:

SELECT INTERVAL '300' month,
       INTERVAL '54-2' year to month,
       INTERVAL ' 11:12:10.1234567' hour to second 
  FROM DUAL;

The output of the above query is:

+25-00,+54-02,+00 11:12:10.1234567

Can someone please explain to me how this query is giving this output, with an explanation about the interval function?

Answer 1

INTERVAL is not a function it's a keyword that introduces an interval literal and such denotes a data type. Similar to what the literals DATE '2011-05-04' or TIMESTAMP '2011-05-04 17:18:19' are doing.

Details about interval literals
http://docs.oracle.com/cd/E11882_01/server.112/e41084/sql_elements003.htm#SQLRF00221
http://docs.oracle.com/cd/E11882_01/server.112/e41084/expressions009.htm#SQLRF52084

Details about the interval datatype:
http://docs.oracle.com/cd/E11882_01/server.112/e41084/sql_elements001.htm#i128552