事务与权限管理

-- 事务示例：转账
START TRANSACTION;

UPDATE accounts SET balance = balance - 100 WHERE id = 1;
UPDATE accounts SET balance = balance + 100 WHERE id = 2;

-- 检查是否成功（应用层判断）
-- 成功则提交，失败则回滚
COMMIT;
-- ROLLBACK;   -- 出错时回滚

-- 隔离级别查看
SELECT @@transaction_isolation;

-- 用户与权限
CREATE USER "reader"@"localhost" IDENTIFIED BY "ReadPass123!";
GRANT SELECT ON school.* TO "reader"@"localhost";

-- 授予多种权限
GRANT SELECT, INSERT, UPDATE ON school.* TO "app_user"@"localhost";

-- 回收权限
REVOKE DELETE ON school.* FROM "app_user"@"localhost";

-- 查看权限
SHOW GRANTS FOR "app_user"@"localhost";

-- 删除用户
DROP USER "reader"@"localhost";

-- 刷新权限（使用 GRANT 语句后通常不需要，修改授权表时需要）
FLUSH PRIVILEGES;