Special function 

There are certain special functions that are not restricted to specific data types.

Syntax

<special function> ::=
  VALUE    ( <expression>, <expression>,...)
| GREATEST ( <expression>, <expression>,...)
| LEAST    ( <expression>, <expression>,...)
| DECODE   ( <check expression>, <search and result spec>,...[, <default expression> ] )

expression, check expression, search and result spec, default expression

VALUE(x,y,...), GREATEST(x,y,...), LEAST(x,y,...), DECODE(x,y,...,z)