CREATE [ OR REPLACE ] FUNCTION [ schema. ] function_name
  [ ( parameter_declaration [, parameter_declaration] )
  ]
  RETURN datatype
  [ { invoker_rights_clause
    | DETERMINISTIC
    | parallel_enable_clause
    | result_cache_clause
    }...
  ]
  { { AGGREGATE | PIPELINED }
    USING [ schema. ] implementation_type
  | [ PIPELINED ] { IS | AS } { [ declare_section ] body | call_spec }
  } ;