MySQL SQL statement optimizes-group by statement optimization

Original: http://bbs.landingbj.com/t-0-243202-1.html

By default, MySQL sorts all group by col1, Col2, ...., and the method of querying is like specifying order by col1, col2, ... in a query.

If you explicitly include an ORDER BY clause that contains the same column, MySQL can optimize it without slowing down, although it is still sorted.

If the query includes group by but you want to avoid the consumption of sort results, you can specify order by NULL to prohibit sorting.

For example:

INSERT into Foo
SELECT A, COUNT (*) from Bar GROUP by a ORDER by NULL;

MySQL SQL statement optimizes-group by statement optimization