在 sql 中计算每行中属性值的出现次数，区分大小写

Question

我有table(notes_subject)结构-

+--------------+-------------+------+-----+---------+----------------+
| Field        | Type        | Null | Key | Default | Extra          |
+--------------+-------------+------+-----+---------+----------------+
| id           | int         | NO   | PRI | NULL    | auto_increment |
| user_id      | int         | NO   |     | NULL    |                |
| note_id      | varchar(25) | NO   | MUL | NULL    |                |
| subject_name | text        | NO   |     | NULL    |                |
+--------------+-------------+------+-----+---------+----------------+

并且数据存储在这个table-

+----+---------+--------------+--------------+
| id | user_id | note_id      | subject_name |
+----+---------+--------------+--------------+
| 10 |       2 | UdMs870BSswp | CN           |
| 12 |       2 | 8stMvslwIGr2 | CN           |
| 13 |       2 | PB3KNbbFkaUm | cn           |
+----+---------+--------------+--------------+

注意：CN 和 cn（小写）不同。

我想计算 user_id 在这个 table 中每个 subject_name 的出现次数。所以我运行查询 -

SELECT subject_name, COUNT(subject_name) 
FROM notes_subject where user_id=2 GROUP BY subject_name;

它获取了 -

+--------------+---------------------+
| subject_name | COUNT(subject_name) |
+--------------+---------------------+
| CN           |                   3 |
+--------------+---------------------+

但这不是正确的结果，因为 CN 和 cn 不同。
我还想要结果中的 id，user_id，note_id。

Answer 1

如果您的数据库支持 window functions，我想您需要这样的东西。尝试使用 collate utf8mb4_bin 看看这是否有助于您需要的区分大小写

select id, 
       user_id, 
       note_id, 
       subject_name, 
       count(subject_name collate utf8mb4_bin) over (partition by user_id, subject_name collate utf8mb4_bin) 
from notes_subject;

如果window functions没有问题，也可以单独聚合，再加入到主table。

DEMO

Answer 2

发布另一个替代方案，由 selecting the group by column as a binary field.

在 dbfiddle 中使用 MYSQL 8.0 版本

进行了测试

SELECT cast(subject_name as binary) subject_name, COUNT(subject_name)  cnt
  FROM notes_subject 
 WHERE user_id=2 
GROUP BY cast(subject_name as binary)

Answer 3

你可以简单地使用二进制来转换它。

SELECT count(*), CAST(subject_name as BINARY) AS lastname_cs 
FROM notes_subject where user_id=2 
GROUP BY CAST(subject_name as BINARY);

在 sql 中计算每行中属性值的出现次数，区分大小写

Count occurence of attribute values in each row with case-sensitive in sql

mysql

sql

case-sensitive