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 7.2.3 Speed of `SELECT' Queries
 -------------------------------
 
 In general, when you want to make a slow `SELECT ... WHERE' query
 faster, the first thing to check is whether you can add an index.  All
 references between different tables should usually be done with
 indexes. You can use the `EXPLAIN' statement to determine which indexes
 are used for a `SELECT'.  See  MySQL indexes MySQL indexes. and
  `EXPLAIN' EXPLAIN.
 
 Some general tips for speeding up queries on `MyISAM' tables:
 
    * To help MySQL optimize queries better, use `ANALYZE TABLE' or run
      `myisamchk --analyze' on a table after it has been loaded with
      data. This updates a value for each index part that indicates the
      average number of rows that have the same value.  (For unique
      indexes, this is always 1.)  MySQL will use this to decide which
      index to choose when you join two tables based on a non-constant
      expression.  You can check the result from the table analysis by
      using `SHOW INDEX FROM TBL_NAME' and examining the `Cardinality'
      value.  `myisamchk --description --verbose' shows index
      distribution information.
 
    * To sort an index and data according to an index, use `myisamchk
      --sort-index --sort-records=1' (if you want to sort on index 1).
      This is a good way to make queries faster if you have a unique
      index from which you want to read all records in order according
      to the index.  Note that the first time you sort a large table
      this way, it may take a long time.
 

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