MySQL的substring_index函數簡析

MySQL的substring_index函數簡析

假定有一張表，其中有個字段是 email 保存了電子郵箱，然後，我想統計每種郵箱的佔比情況。

我們知道電子信箱的格式是： account@domain ，要實現上面的統計，必須取得 email
字符串中 @ 後面的域名部分。

MySQL提供了一個名爲 substring_index 的函數，能夠滿足我們的需求：

MySQL 5.5 Reference Manual 寫道  www.2cto.com  

SUBSTRING_INDEX(str,delim,count)

Returns the substring from string str before count occurrences of the delimiter delim.
If count is positive, everything to the left of the final delimiter (counting from the left)
is returned. If count is negative, everything to the right of the final delimiter (counting
from the right) is returned. SUBSTRING_INDEX() performs a case-sensitive match when
searching for delim.

mysql> SELECT SUBSTRING_INDEX('www.mysql.com', '.', 2);

       -> 'www.mysql'

mysql> SELECT SUBSTRING_INDEX('www.mysql.com', '.', -2);

       -> 'mysql.com'

This function is multi-byte safe.

  www.2cto.com  

查詢語句如下：

Sql代碼  

select  

   substring_index(email,'@',-1) as domain,  

   count(distinct email) as count,  

   count(distinct email)  

       / (select count(distinct email) from qzt_resume_basic where email like '%@%')  

       * 100 as percent  

from qzt_resume_basic  

where email like '%@%'  

group by 1  

order by 2 desc  

limit 10;