The MONTHS_BETWEEN(date 1, date 2) function returns the number of months between two dates:
months_between('01-FEB-2008', '01-JAN-2008') = 1
The DECODE Function
Although its name sounds mysterious, this function is straightforward. The DECODE function implements if then-else conditional logic by testing its first two terms for equality and returns the third if they are equal and optionally returns another term if they are not.
DECODE Function Facilitates conditional inquiries by doing the work of a CASE expression or an IF-THENELSE statement:
DECODE(col|expression, search1, result1
[, search2, result2, ..., ]
[, default])
DECODE Function
The DECODE function decodes an expression in a way similar to the IF-THEN-ELSE logic that is used in various languages. The DECODE function decodes expression after comparing it to each search value. If the expression is the same as search, result is returned.
If the default value is omitted, a null value is returned where a search value does not match any of the result values.