#表的结构 test3
CREATE TABLE IF NOT EXISTS test3 (id int(11) NOT NULL auto_increment,bid int(11) NOT NULL,cid int(11) NOT NULL,dtime datetime NOT NULL,
PRIMARY KEY (id)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=6 ;
# Transfer data stored in the table test3
INSERT INTO test3 (id, bid, cid, dtime) VALUES
(1, 1, 3, ‘2014-03-18 16:00:00’),
(2, 1, 10, ‘2014-03-18 17:00:00’),
(3, 2, 5, ‘2014-03-18 18:00:00’),
(4, 2, 6, ‘2014-03-18 19:00:00’),
(5, 1, 7, ‘2014-03-18 20:00:00’);
Second, by subqueries
1, sql statement
select from(select from test3 ORDER BY dtime DESC) as temp GROUP BY bid ORDER BY dtime DESC;
So the question is
Some computer bid = 1 is set 5.7mysql 16:00, 5.67mysql is 20 points, that is opposite to the
By explain view the execution plan, you can see there is no limit of time, one less DERIVED internal operations is estimated to be optimized, that the ORDER BY syntax in which there is negligible LIMIT restrictions involving the result of the sort, do not ignore the ORDER BY, can achieve the desired
test it,
the SELECT from (the SELECT from Test3 the ORDER BY DESC limit DTIME 999999999) AS the TEMP Bid the ORDER BY DTIME the GROUP BY
can, however inelegant
official website information
https://dev.mysql.com/doc/refman/5.7 /en/group-by-handling.html
description official website
may also be so
SELECT from (SELECT the DISTINCT from the ORDER BY Test3 DTIME DESC) AS TEMP Bid the GROUP BY the ORDER BY ID desc