Null correlation function

1. NVL (EXPR1,EXPR2) returns EXPR2 if expr is empty

Select nvl (e.commission_pct, one from Employees e;  -- If the bonus is empty, return one

2. NVL2 (EXPR1,EXPR2,EXPR3) returns EXPR3 if EXPR1 returns EXPR2 NOT NULL

Select + 1  One )  from-- +1 If the wage is not empty, returns one by one

3. LNNVL (expr) returns true if expr is false, or if the word blank is judged within expr

  Select *  from Employees e   where > 0.2 -- query bonuses are empty and bonuses are not greater than 0.2 of employee information

4. NANVL (N1,N2)

5.nullif (EXPR1,EXPR2) returns null if EXPR1 equals EXPR2, otherwise returns EXPR1

   Select Nullif (' A ' a 'nullif('a'  'b'from-- query result is empty and a

6. COALESCE (EXPR1,EXPR2 ...) returns the value of the first non-empty expression, with at least two arguments, if no query to non-empty data returns null

Select COALESCE (null NULL null-NULLCOALESCE(nullnull NULL )     from-- query result is 14 and null

Null correlation function