General functions are of the following types :
NVL : Converts a null value to an actual value. NVL (exp1, exp2) .If exp1 is null then the NVL function returns the value of exp2.
NVL2 : If exp1 is not null, nvl2 returns exp2, if exp1 is null, nvl2 returns exp3. The argument exp1 can have any data type. NVL2 (exp1, exp2, exp3)
NULLIF : Compares two expressions and returns null if they are equal or the first expression if they are not equal. NULLIF (exp1, exp2)
COALESCE : Returns the first non-null expression in the expression list. COALESCE (exp1, exp2… expn). The advantage of the COALESCE function over the NVL function is that the COALESCE function can take multiple alternative values.
Conditional Expressions : Provide the use of IF-THEN-ELSE logic within a SQL statement. Example: CASE Expression and DECODE Function.
