简单了解添加mysql索引的3条原则

//准备二张测试表 
mysql> CREATE TABLE `test_t` ( 
-> `id` int(11) NOT NULL auto_increment, 
-> `num` int(11) NOT NULL default '0', 
-> `d_num` varchar(30) NOT NULL default '0', 
-> PRIMARY KEY (`id`) 
-> ) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ; 
Query OK, 0 rows affected (0.05 sec) 
mysql> CREATE TABLE `test_test` ( 
-> `id` int(11) NOT NULL auto_increment, 
-> `num` int(11) NOT NULL default '0', 
-> PRIMARY KEY (`id`) 
-> ) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ; 
Query OK, 0 rows affected (0.05 sec) 
//创建一个存储过程，为插数据方便 
mysql> delimiter | 
mysql> create procedure i_test(pa int(11),tab varchar(30)) 
-> begin 
-> declare max_num int(11) default 100000; 
-> declare i int default 0; 
-> declare rand_num int; 
-> declare double_num char; 
-> 
-> if tab != 'test_test' then 
-> select count(id) into max_num from test_t; 
-> while i < pa do 
-> if max_num < 100000 then 
-> select cast(rand()*100 as unsigned) into rand_num; 
-> select concat(rand_num,rand_num) into double_num; 
-> insert into test_t(num,d_num)values(rand_num,double_num); 
-> end if; 
-> set i = i +1; 
-> end while; 
-> else 
-> select count(id) into max_num from test_test; 
-> while i < pa do 
-> if max_num < 100000 then 
-> select cast(rand()*100 as unsigned) into rand_num; 
-> insert into test_test(num)values(rand_num); 
-> end if; 
-> set i = i +1; 
-> end while; 
-> end if; 
-> end| 
Query OK, 0 rows affected (0.00 sec) 
mysql> delimiter ; 
mysql> show variables like "%pro%"; //查看一下，记录执行的profiling是不是开启动了，默认是不开启的 
+---------------------------+-------+ 
| Variable_name | Value | 
+---------------------------+-------+ 
| profiling | OFF | 
| profiling_history_size | 15 | 
| protocol_version | 10 | 
| slave_compressed_protocol | OFF | 
+---------------------------+-------+ 
4 rows in set (0.00 sec) 
mysql> set profiling=1; //开启后，是为了对比加了索引后的执行时间 
Query OK, 0 rows affected (0.00 sec)