根据doc http://dev.mysql.com/doc/refman/5.0/en/server-status-variables.html#statvar_Connections

连接

尝试连接MySQL服务器的次数(成功或失败)。

SHOW STATUS WHERE `variable_name` = 'Threads_connected';

这将显示所有打开的连接。

这是到目前为止到服务器的连接总数。 要查找当前连接状态，可以使用

Mysqladmin -u -p extended-status | grep -wi 'threads_connected\|threads_running' | awk '{打印$2，$4}'

这将告诉你:

Threads_connected 12

Threads_running 1  

Threads_connected: Number of connections

Threads_running: connections currently running some sql

你也可以

SHOW STATUS WHERE `variable_name` = 'Max_used_connections';

它应该是当前活动连接的数量。运行processlist命令确认。

参考网址:http://www.devdaily.com/blog/post/mysql/how-show-open-database-connections-mysql

编辑:打开的DB连接数请看这里，实际的线程(连接)数描述在这里!

根据文档，它指的是历史上的总数:

连接 尝试连接MySQL服务器的次数(成功或失败)。

您可以通过Threads_connected状态变量查看活动连接的数量:

Threads_connected 当前打开的连接数。

mysql> show status where `variable_name` = 'Threads_connected';
+-------------------+-------+
| Variable_name     | Value |
+-------------------+-------+
| Threads_connected | 4     |
+-------------------+-------+
1 row in set (0.00 sec)

．.． 或者通过show processlist命令:

mysql> show processlist;
+----+------+-----------------+--------+---------+------+-------+------------------+
| Id | User | Host            | db     | Command | Time | State | Info             |
+----+------+-----------------+--------+---------+------+-------+------------------+
|  3 | root | localhost       | webapp | Query   |    0 | NULL  | show processlist | 
|  5 | root | localhost:61704 | webapp | Sleep   |  208 |       | NULL             | 
|  6 | root | localhost:61705 | webapp | Sleep   |  208 |       | NULL             | 
|  7 | root | localhost:61706 | webapp | Sleep   |  208 |       | NULL             | 
+----+------+-----------------+--------+---------+------+-------+------------------+
4 rows in set (0.00 sec)