MySQL查询当前连接数的语句

1. 查看当前总连接数

SHOW STATUS LIKE 'Threads_connected';

• 返回当前建立的连接总数

2. 查看最大连接数配置

SHOW VARIABLES LIKE 'max_connections';

• 显示服务器允许的最大并发连接数

3. 查看详细的连接信息

SHOW PROCESSLIST;

• 显示所有连接的详细信息（用户、来源IP、执行的SQL等）

4. 按用户分组统计连接数

SELECT user, COUNT(*) as connections
FROM information_schema.processlist
GROUP BY user;

5. 查看连接数使用率

SELECT
  (SELECT VARIABLE_VALUE
   FROM performance_schema.global_status
   WHERE VARIABLE_NAME = 'Threads_connected') AS current_connections,

  (SELECT VARIABLE_VALUE
   FROM performance_schema.global_variables
   WHERE VARIABLE_NAME = 'max_connections') AS max_connections,

  ROUND((SELECT VARIABLE_VALUE
         FROM performance_schema.global_status
         WHERE VARIABLE_NAME = 'Threads_connected') /
        (SELECT VARIABLE_VALUE
         FROM performance_schema.global_variables
         WHERE VARIABLE_NAME = 'max_connections') * 100, 2) AS connection_usage_rate;

6. 查看不同状态的连接数

SELECT command, COUNT(*)
FROM information_schema.processlist
GROUP BY command;

7. 查看空闲连接数（Sleep状态）

SELECT COUNT(*)
FROM information_schema.processlist
WHERE command = 'Sleep';

注意事项：

1. 需要至少 PROCESS 权限才能查看所有连接
2. 生产环境连接数接近 max_connections 时需要扩容或优化
3. 长时间 Sleep 的连接可以考虑适当调低 wait_timeout 参数

如果需要终止连接，可以使用：

KILL [connection_id];  -- 从SHOW PROCESSLIST结果中获取ID