MySQL 5.6 Reference Manual Including MySQL NDB Cluster 7.3-7.4 Reference Guide
ANALYSE([
max_elements
[,max_memory
]])
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:
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.
max_memory
(default 8192) is
the maximum amount of memory that
ANALYSE()
should allocate per column
while trying to find all distinct values.
A PROCEDURE
clause is not permitted in a
UNION
statement.