這個函數的主要目的是將null值替換成爲另一個值。sql
The NVL function is used to replace NULL values by another value.
The syntax for the NVL function is:
NVL( value_in, replace_with )
value_in if the function to test on null values. The value_in field can have a datatype char, varchar2, date or number datatype.
replace_with is the value that is returned if value_in has a null value. The NVL statement works like this pl/sql code:函數
if (value_in is NULL) then return replace_with; else return value_in; end if; Sample code: select nvl(salary, 0) from employees; select nvl(ref_code,'Unknown') from users;