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:
max_elements(default 256) is the maximum number of distinct values thatANALYSE()notices per column. This is used byANALYSE()to check whether the optimal data type should be of typeENUM; if there are more thanmax_elementsdistinct values, thenENUMis not a suggested type.max_memory(default 8192) is the maximum amount of memory thatANALYSE()should allocate per column while trying to find all distinct values.