[20190910] descending index on the issue 5.txt

[20190910] descending indexes on the issue 5.txt

- // index TERM tested using 0xfe said the recall special character encoding issues previously encountered in descending order of the index, but now forgotten.
- // Now think about was how out of their own guess, ^ _ ^.
- // link: http: //blog.itpub.net/267265/viewspace-2221527/ => [20181124 ] 2.txt descending indexes on the issue

- then // summary:
- // short point is that sort needs, out of a pit (ending plus FF), and to enter into a deeper pit, occupation chr (0) code, and chr (0) and occupied chr (1) of the code, and enter
- a deeper // pit. The results appear this special code, in fact, some developers to provide some reference, see how oracle technical personnel to achieve these, although I do not know as
- // how to write the code.

- // make a record again:
ASCII code coding
-------------------------------------- -------
0x00 FEFE
0x0000 FEFD
0x0001 FEFC
0x00NN (0xNN> = 0x02) FEFB (Note: 0x00 encoding means in front, seen here again a little halo)
0x01 Fefa
0x0100 FEF9
0x0101                  FEF8        
0x01NN(0xNN>=0x02)      FEF7(注:指前面0x01编码)
---------------------------------------------

WITH x0
     AS ( SELECT '00' a, CHR (0) b FROM DUAL
         UNION ALL
         SELECT '01', CHR (1) FROM DUAL
         union all
         SELECT '02', CHR (2) FROM DUAL
         )
select * from (
SELECT x1.a || x2.a c10, sys_op_descend (x1.b || x2.b) c20  FROM x0 x1, x0 x2
union all
SELECT x1.a c10, sys_op_descend (x1.b) c20 FROM x0 x1 ) order by c10 ;

C10        C20
---------- --------------------
00         FEFEFF
0000       FEFDFF
0001       FEFCFF
0002       FEFBFDFF
01         FEFAFF
0100       FEF9FF
0101       FEF8FF
0102       FEF7FDFF
02         FDFF
0200       FDFEFEFF
0201       FDFEFAFF
0202       FDFDFF
12 rows selected.