mysql函数的使用

最近总感觉sql语句不对劲，所以就看了一些官方文档发现了一些以前没有注意的函数：感觉在查询的时候可以用得上，毕竟是内置函数，用起来效率应该会好一些的：

FIND_IN_SET(str,strlist)

mysql> SELECT FIND_IN_SET('b','a,b,c,d');
        -> 2

如：SELECT FIND_IN_SET(a.roleId,r.roleName), a.* from t_admin a ,t_role r where a.roleId = r.roleId AND FIND_IN_SET(a.roleId,r.roleId);

代替in、not in

INSTR(str,substr)

mysql> SELECT INSTR('foobarbar', 'bar');
        -> 4

如：select a.* FROM  t_admin a where INSTR(a.account,'发达');

可以用于模糊查询 代替like  提高效率

LOCATE(substr,str), LOCATE(substr,str,pos)

mysql> SELECT LOCATE('xbar', 'foobar');
        -> 0
mysql> SELECT LOCATE('bar', 'foobarbar', 5);
        -> 7

select a.* FROM  t_admin a where LOCATE('发达',a.account);

可以用于模糊查询 代替like  提高效率

• select  
      substring_index(email,'@',-1) as domain,  
      count(distinct email) as count,  
      count(distinct email)  
          / (select count(distinct email) from t_user where email like '%@%')  
          * 100 as percent  
  from t_user  
  where email like '%@%'   
  group by 1   
  order by 3 ASC   
  limit 10;

select
    substring_index(email,'@',-1) as domain,
    count(distinct email) as count,
    count(distinct email)
        / (select count(distinct email) from t_user where email like '%@%')
        * 100 as percent
from t_user
where email like '%@%'
group by 1
order by 3 ASC
limit 10;