CREATE TABLE history_tmp (
	itemid		bigint unsigned		DEFAULT '0'	NOT NULL,
	clock		integer		DEFAULT '0'	NOT NULL,
	value		double(16,4)		DEFAULT '0.0000'	NOT NULL
) ENGINE=InnoDB;
CREATE INDEX history_1 on history_tmp (itemid,clock);

insert into history_tmp select * from history;
drop table history;
alter table history_tmp rename history;