MySQL中行级锁和表级锁的区别小结

START TRANSACTION;

-- 获取共享锁
SELECT * FROM employees WHERE id = 1 LOCK IN SHARE MODE;

-- 完成事务
COMMIT;

START TRANSACTION;

-- 获取排它锁
SELECT * FROM employees WHERE id = 1 FOR UPDATE;

-- 完成事务
COMMIT;

LOCK TABLES employees READ;

-- 在锁定的表上执行读操作
SELECT * FROM employees;

-- 释放锁
UNLOCK TABLES;

LOCK TABLES employees WRITE;

-- 在锁定的表上执行写操作
INSERT INTO employees (name, department_id) VALUES ('Alice', 1);

-- 释放锁
UNLOCK TABLES;

CREATE TABLE employees (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(255) NOT NULL,
    department_id INT NOT NULL,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
) ENGINE=InnoDB;

INSERT INTO employees (name, department_id) VALUES ('Alice', 1), ('Bob', 2);

START TRANSACTION;
UPDATE employees SET name = 'Charlie' WHERE id = 1;
-- 保持事务未提交

START TRANSACTION;
UPDATE employees SET name = 'Dave' WHERE id = 2;
-- 保持事务未提交

CREATE TABLE employees (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(255) NOT NULL,
    department_id INT NOT NULL,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
) ENGINE=MyISAM;

INSERT INTO employees (name, department_id) VALUES ('Alice', 1), ('Bob', 2);

LOCK TABLES employees WRITE;
UPDATE employees SET name = 'Charlie' WHERE id = 1;
-- 保持锁未释放

-- 会被阻塞，直到会话 1 释放锁
LOCK TABLES employees WRITE;
UPDATE employees SET name = 'Dave' WHERE id = 2;