猿是人类的好朋友

​​SELECT shuming FROM test WHERE pingjia=‘好’ GROUP BY shuming ORDER BY COUNT(shuming) DESC LIMIT 1;SELECT COUNT(DISTINCT(shuming)) FROM test;

SELECT shuming FROM test WHERE pingjia='好' GROUP BY shuming ORDER BY COUNT(shuming) DESC LIMIT 1;SELECT COUNT(DISTINCT(shuming)) FROM test;

索引下推有了索引下推优化，可以在有like条件查询的情况下，减少回表次数。对于user_table表，我们现在有（username,age）联合索引如果现在有一个需求，查出名称中以“张”开头且年龄小于等于10的用户信息，语句如下：select * from user_table where username like '张%' and age > 101语句有两种执行可能：根据（username,age）联合索引查询所有满足名称以“张”开头的索引，然后回表查询出相应的全行数据，然