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占比情況。
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提供了一個名為 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;
作者 codingstandards
