General Functions

• NVL(expr1, expr2)
  Converts a null value to an actual value(expr2)
  
• NVL2(expr1,expr2,expr3)
  If expr1 is not null, NVL2 returns expr2. If expr1 is null, NVL2 returns expr3. The argument expr1 can have any data type.
  
• NULLIF(expr1, expr2)
  Compares two expressions and returns null if they are equal; returns the first expression if they are not equal.
  
• COALESCE(expr1,expr2, ... expr n)
  Returns the first non-null expression in the expression list.