Syntax:
ANALYSE([max_elements[,max_memory]])

ANALYSE() is defined in the sql/sql_analyse.cc source file, which
serves as an example of how to create a procedure for use with the
PROCEDURE clause of SELECT statements. ANALYSE() is built in and is
available by default; other procedures can be created using the format
demonstrated in the source file.

ANALYSE() examines the result from a query and returns an analysis of
the results that suggests optimal data types for each column that may
help reduce table sizes. To obtain this analysis, append PROCEDURE
ANALYSE to the end of a SELECT statement:

SELECT ... FROM ... WHERE ... PROCEDURE ANALYSE([max_elements,[max_memory]])

For example:

SELECT col1, col2 FROM table1 PROCEDURE ANALYSE(10, 2000);

The results show some statistics for the values returned by the query,
and propose an optimal data type for the columns. This can be helpful
for checking your existing tables, or after importing new data. You may
need to try different settings for the arguments so that PROCEDURE
ANALYSE() does not suggest the ENUM data type when it is not
appropriate.

The arguments are optional and are used as follows:

o max_elements (default 256) is the maximum number of distinct values
  that ANALYSE() notices per column. This is used by ANALYSE() to check
  whether the optimal data type should be of type ENUM; if there are
  more than max_elements distinct values, then ENUM is not a suggested
  type.

o max_memory (default 8192) is the maximum amount of memory that
  ANALYSE() should allocate per column while trying to find all
  distinct values.

URL: http://dev.mysql.com/doc/refman/5.5/en/procedure-analyse.html

