The return data type of Decode and NVL are......

Decode function return data type is always the same as its first returned argument.

select decode(hiredt,09-SEP-1979,NULL,hiredt)

In the above case the return data type is VARCHAR2, since NULL has a VARCHAR2 data type. In the above case, we can make sure that the return data type is date, by applying a to_date function on the null value.

select decode(hiredt,09-SEP-1979,to_date(NULL),hiredt)

Similarly NVL \'s return datatype is the same datatype as its first returned argument.

Answer : It is the same datatype as its first returned argument.