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Return different values based on the content of a column/expression.
   decode(expression, search1, return1,
                      [search2, return2]...
                      [default] )
e.g.
   SELECT decode(sex, 'M', 'Male',
                      'F', 'Female', 'Unknown')
   FROM   employees;
 You can convert a character or expression 
  that contains a number into an actual number value.
  
  The 'format' must be a valid Number format.
  
  nls_lang allows international formats to be applied e.g. currency symbols and 
  numeric chars.
  
  See Also
  
  CASE function