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  • 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; 



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  • 原文地址:https://www.cnblogs.com/snake-hand/p/3206550.html
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