MySQL操作(四)索引及优化

-- 1、查看表的索引
SHOW INDEX FROM ebh_roomsms;

-- 2、添加PRIMARY KEY（主键索引） 
mysql>ALTER TABLE `table_name` ADD PRIMARY KEY ( `column` ) 

-- 3、添加UNIQUE(唯一索引) 
mysql>ALTER TABLE `table_name` ADD UNIQUE ( `column` ) 

-- 4、添加INDEX(普通索引) 
mysql>ALTER TABLE `table_name` ADD INDEX index_name ( `column` ) 
-- 例：ALTER TABLE `ebh_users` ADD INDEX initpwd (`initpwd`) 

-- 5、添加FULLTEXT(全文索引) 
mysql>ALTER TABLE `table_name` ADD FULLTEXT ( `column`) 
-- 6、添加多列索引 
mysql>ALTER TABLE `table_name` ADD INDEX index_name ( `column1`, `column2`, `column3` )

EXPLAIN SELECT count(0) count,if(sex=0,‘男‘,‘女‘) sex,avg(balance),(case when balance<1000 then ‘1000以下‘ when balance BETWEEN 1000 and 5000 then ‘1000-5000‘ else ‘5000以上‘ end) as `level` from ebh_users where sex<2  GROUP BY `level`,sex;