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    1. General Information
    2. MySQL Installation
    3. Tutorial Introduction
    4. Database Administration
    5. MySQL Optimisation
    6. MySQL Language Reference
    7. MySQL Table Types
    8. MySQL APIs
    9. Extending MySQL
    504 MySQL Technical Reference for Version 4.0.3    If you use ALTER TABLE to rst add an UNIQUE index to a table used in a MERGE table and then use ALTER TABLE to add a normal index on the MERGE table, the key order will be di erent for the tables if there was an old non-unique key in the table.  This is because ALTER TABLE  puts  UNIQUE  keys before normal keys to be able to detect duplicate keys as early as possible.    The range optimiser can't yet use  MERGE  table eciently and may sometimes produce non-optimal joins.  This will be xed in MySQL 4.0.x.    DROP TABLE  on  a  table  that  is  in  use  by  a  MERGE  table  will  not  work  on  Windows because  the  MERGE  handler  does  the  table  mapping  hidden  from  the  upper  layer  of MySQL. Because Windows doesn't allow you to drop les that are open, you rst must ush all  MERGE  tables (with  FLUSH TABLES) or drop the  MERGE  table before dropping the table.  We will x this at the same time we introduce VIEWs. 7.3  ISAM Tables You can also use the deprecated ISAM table type.  This will disappear rather soon (probably in MySQL 4.1) because  MyISAM  is a better implementation of the same thing.  ISAM  uses a B-tree index.  The index is stored in a le with the `.ISM' extension, and the data is stored in  a   le  with  the  `.ISD'  extension.   You  can  check/repair  ISAM  tables  with  the  isamchk utility.  See Section 4.4.6.7 [Crash recovery], page 237. ISAM has the following features/properties:    Compressed and xed-length keys    Fixed and dynamic record length    16 keys with 16 key parts/key    Max key length 256 (default)    Data is stored in machine format; this is fast, but is machine/OS dependent. Most of the  things true for  MyISAM  tables  are also  true for  ISAM  tables.   See  Section 7.1 [MyISAM], page 494.  The major di erences compared to MyISAM tables are:    ISAM tables are not binary portable across OS/Platforms.    Can't handle tables > 4G.    Only support pre x compression on strings.    Smaller key limits.    Dynamic tables get more fragmented.    Tables are compressed with pack_isam rather than with myisampack. If you want to convert an ISAM table to a MyISAM table so that you can use utilities such as mysqlcheck, use an  ALTER TABLE  statement: mysql> ALTER TABLE tbl_name TYPE = MYISAM; The embedded MySQL versions doesn't support ISAM tables.
     

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