mysql 按相似度来排序

数据库tag字段内容格式：a,b,c,d ...
假设有这几条记录
1：刘世允
2：郑胜浩
3：申东烨
4: 申东烨,郑胜浩,刘世允,安英美
5: 郑胜浩,刘世允,安英美
6: 申东烨,郑胜浩
7：刘世允,安英美

给出的查询tag
$tag = '申东烨,郑胜浩,刘世允,安英美,李尚勋';
按照相同词的个数排序

查询的结果
1: 申东烨,郑胜浩,刘世允,安英美
2: 郑胜浩,刘世允,安英美
3: 申东烨,郑胜浩
4：刘世允,安英美
5：刘世允
6：郑胜浩
7：申东烨

回复内容：

数据库tag字段内容格式：a,b,c,d ...
假设有这几条记录
1：刘世允
2：郑胜浩
3：申东烨
4: 申东烨,郑胜浩,刘世允,安英美
5: 郑胜浩,刘世允,安英美
6: 申东烨,郑胜浩
7：刘世允,安英美

给出的查询tag
$tag = '申东烨,郑胜浩,刘世允,安英美,李尚勋';
按照相同词的个数排序

查询的结果
1: 申东烨,郑胜浩,刘世允,安英美
2: 郑胜浩,刘世允,安英美
3: 申东烨,郑胜浩
4：刘世允,安英美
5：刘世允
6：郑胜浩
7：申东烨

----------------建表

<code class="lang-sql">mysql> create table testsort (tag varchar(100) charset "GBK");
Query OK, 0 rows affected (0.51 sec)
</code>

```sql
mysql> describe testsort
-> ;
+-------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| tag | varchar(100) | YES | | NULL | |
+-------+--------------+------+-----+---------+-------+
1 row in set (0.07 sec)

<code><br>----------------插入数据
```sql
mysql> insert into testsort(id,tag) values(1,"刘世允"),
    -> (2,"郑胜浩"),
    -> (3,"申东烨"),
    -> (4,"申东烨,郑胜浩,刘世允,安英美"),
    -> (5,"郑胜浩,刘世允,安英美"),
    -> (6,"申东烨,郑胜浩"),
    -> (7,"刘世允,安英美");
Query OK, 7 rows affected (0.07 sec)
Records: 7  Duplicates: 0  Warnings: 0
</code>

----------------方法

<code class="lang-sql">mysql> select id,
    -> tag,
    -> char_length(tag)-char_length(replace(tag,',',''))+1 as cnt
    -> from testsort;
+------+-----------------------------------------+------+
| id   | tag                                     | cnt  |
+------+-----------------------------------------+------+
|    1 | 刘世允                                  |    1 |
|    2 | 郑胜浩                                  |    1 |
|    3 | 申东烨                                  |    1 |
|    4 | 申东烨,郑胜浩,刘世允,安英美             |    4 |
|    5 | 郑胜浩,刘世允,安英美                    |    3 |
|    6 | 申东烨,郑胜浩                           |    2 |
|    7 | 刘世允,安英美                           |    2 |
+------+-----------------------------------------+------+
7 rows in set (0.00 sec)

</code>

----------------另外注意
Responses below will get you there. However, don't forget to use CHAR_LENGTH() instead of LENGTH() if you're using multibyte characters. – inhan Sep 10 '12 at 3:03

http://stackoverflow.com/questions/12344795/count-the-number-of-occurences-of-a-string-in-a-varchar-field