[MySQL] MySQL的索引，你真的有好好理解过吗？

#创建表 
CREATE TABLE `test` ( 
`id` int(11) NOT NULL, 
`a` int(11) NOT NULL default 0, 
`b` int(11) NOT NULL default 0, 
PRIMARY KEY (`id`), 
KEY `a` (`a`), 
KEY `b` (`b`) 
) ENGINE=InnoDB; 

#添加数据 
delimiter ;; 
create procedure xddata() 
begin 
declare i int; 
set i=1; 
while(i<=100000)do 
insert into test values(i, i, i); 
set i=i+1; 
end while; 
end;; 
delimiter ; 
call xddata(); 

数据查询 
explain select * from test where (a between 1000 and 2000) and (b between 50000 and 100000) order by b limit 1;

select * from test where (a between 1000 and 2000) and (b between 50000 and 100000) order by b limit 1; 

select * from test force index(a) where (a between 1000 and 2000) and (b between 50000 and 100000) order by b limit 1;