Questions on index and 'order by'

[Bernard Chambon]

I try to understand index usage for 'order by'
but that's seemn hard to me.
Here is what I have tried :
1_ About documentation
I have read carefully related documentation (7.2.9  How MySQL Optimizes  
ORDER BY) but
I don't understand it.
 - What is the difference betwween 'key1' and 'key_part1' ?
 - Why is it written ? :
   The following query will use the index to resolve the ORDER BY
     SELECT * FROM t1 WHERE key_part1=constant ORDER BY key_part2

   The following query cannot use indexes to resolve the ORDER BY
     SELECT * FROM t1 WHERE key2=constant ORDER BY key_part2;
2_ I also tried a small example (table Test), with 2 fields and 2  
(multiple) indexes

     create table Test(Name varchar(64),  Adress varchar(128), \
                       index K0(Name(16), Adress(16)), \
                       index K1(Adress(16), Name(16)) ) type = INNOBASE  
 ;

   What are the indexes needed for 'orber by' in the  request
      select * from Test  where Name='n1'  order by Adress ;
   If I ask explain, I got 'Using filesort' in Extra column information
    mysql> explain select * from Test  where Name='n1'  order by Adress  
;
     
+-------+------+---------------+------+---------+-------+------ 
+-----------------------------+
    | table | type | possible_keys | key  | key_len | ref   | rows |  
Extra                       |
     
+-------+------+---------------+------+---------+-------+------ 
+-----------------------------+
    | Test  | ref  | K0            | K0   |      17 | const |    1 |  
Using where; Using filesort |
     
+-------+------+---------------+------+---------+-------+------ 
+-----------------------------+

Thanks for any help
-------------------------
Bernard Chambon
IN2P3 / CNRS
[EMAIL PROTECTED]
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