MySQL 很实用的 SQL 语句清单（排障与日常运维）

这篇只放"能直接用"的 SQL，小而实用，适合收藏。

一、查看连接与慢查询

sql 复制代码

-- 当前连接
SHOW PROCESSLIST;

-- 只看活跃中的 SQL
SELECT * FROM information_schema.PROCESSLIST
WHERE COMMAND <> 'Sleep'
ORDER BY TIME DESC;

-- 慢查询是否开启
SHOW VARIABLES LIKE 'slow_query_log';
SHOW VARIABLES LIKE 'long_query_time';

-- 最近慢查询文件位置
SHOW VARIABLES LIKE 'slow_query_log_file';

二、查看表大小与空间占用

sql 复制代码

SELECT
  table_schema,
  table_name,
  ROUND((data_length + index_length) / 1024 / 1024, 2) AS size_mb
FROM information_schema.TABLES
WHERE table_schema = 'your_db'
ORDER BY size_mb DESC;

三、查看索引使用情况

sql 复制代码

-- 某表索引
SHOW INDEX FROM your_table;

-- 索引列顺序（组合索引很关键）
SELECT
  index_name,
  seq_in_index,
  column_name
FROM information_schema.STATISTICS
WHERE table_schema = 'your_db'
  AND table_name = 'your_table'
ORDER BY index_name, seq_in_index;

四、找出无主键表

sql 复制代码

SELECT t.table_schema, t.table_name
FROM information_schema.TABLES t
LEFT JOIN information_schema.TABLE_CONSTRAINTS c
  ON t.table_schema = c.table_schema
 AND t.table_name = c.table_name
 AND c.constraint_type = 'PRIMARY KEY'
WHERE t.table_schema = 'your_db'
  AND c.constraint_name IS NULL;

五、查看锁等待（排查阻塞）

sql 复制代码

-- InnoDB 锁等待
SELECT
  r.trx_id waiting_trx_id,
  r.trx_mysql_thread_id waiting_thread,
  r.trx_query waiting_query,
  b.trx_id blocking_trx_id,
  b.trx_mysql_thread_id blocking_thread,
  b.trx_query blocking_query
FROM information_schema.INNODB_LOCK_WAITS w
JOIN information_schema.INNODB_TRX r ON r.trx_id = w.requesting_trx_id
JOIN information_schema.INNODB_TRX b ON b.trx_id = w.blocking_trx_id;

六、查重复数据（最常用）

sql 复制代码

-- 查 user_id + mobile 的重复
SELECT user_id, mobile, COUNT(*) AS cnt
FROM user
GROUP BY user_id, mobile
HAVING cnt > 1;

七、批量去重（保留最小 id）

sql 复制代码

DELETE t1
FROM user t1
JOIN user t2
  ON t1.user_id = t2.user_id
 AND t1.mobile = t2.mobile
 AND t1.id > t2.id;

八、找出最近 N 天未更新的数据

sql 复制代码

SELECT *
FROM orders
WHERE update_time < NOW() - INTERVAL 30 DAY;

九、分页优化模板（避免深分页）

sql 复制代码

-- 基于游标翻页
SELECT id, create_time
FROM orders
WHERE (create_time < '2026-04-01 10:00:00'
   OR (create_time = '2026-04-01 10:00:00' AND id < 9527))
ORDER BY create_time DESC, id DESC
LIMIT 20;

十、快速生成批量插入语句

sql 复制代码

INSERT INTO dict (type, code, name) VALUES
('status', '0', '禁用'),
('status', '1', '启用'),
('status', '2', '删除');

十一、查看表行数（估算）

sql 复制代码

SELECT table_name, table_rows
FROM information_schema.TABLES
WHERE table_schema = 'your_db'
ORDER BY table_rows DESC;

十二、找出表里"最常见的值"

sql 复制代码

SELECT status, COUNT(*) AS cnt
FROM orders
GROUP BY status
ORDER BY cnt DESC
LIMIT 5;

最后总结

这份 SQL 清单不是"概念"，而是我日常排障和运维最常用的那一批。

你可以直接复制用，遇到具体场景再精细化调整。