快速参考
这是一份 SQL 常用语句的速查表，覆盖日常开发 90% 的场景。需要时直接复制改表名和条件即可。
数据库操作：
CREATE DATABASE feixiang_db;
DROP DATABASE feixiang_db;
USE feixiang_db;
SHOW DATABASES;
表操作：
CREATE TABLE employees (emp_id INT PRIMARY KEY, emp_name VARCHAR(50), salary DECIMAL(10,2));
ALTER TABLE employees ADD COLUMN email VARCHAR(100);
ALTER TABLE employees MODIFY COLUMN salary DECIMAL(12,2);
ALTER TABLE employees DROP COLUMN email;
DROP TABLE employees;
TRUNCATE TABLE employees;
SHOW TABLES;
DESCRIBE employees;
增删改查：
-- 增
INSERT INTO employees (emp_name, salary) VALUES ('翱翔', 8888.88);
INSERT INTO employees VALUES (10001, '翱翔', 8888.88), (10002, '飞翔', 20000.00);
-- 删
DELETE FROM employees WHERE emp_id = 10001;
-- 改
UPDATE employees SET salary = 10000 WHERE emp_name = '翱翔';
-- 查
SELECT * FROM employees;
SELECT emp_name, salary FROM employees WHERE dept_code = 2;
SELECT DISTINCT dept_code FROM employees;
SELECT * FROM employees ORDER BY salary DESC LIMIT 10;
聚合与分组：
SELECT COUNT(*) FROM employees;
SELECT AVG(salary) FROM employees WHERE dept_code = 2;
SELECT dept_code, AVG(salary) FROM employees GROUP BY dept_code;
SELECT dept_code, AVG(salary) FROM employees GROUP BY dept_code HAVING AVG(salary) > 10000;
连接查询：
SELECT e.emp_name, d.dept_name FROM employees e INNER JOIN departments d ON e.dept_code = d.dept_id;
SELECT e.emp_name, d.dept_name FROM employees e LEFT JOIN departments d ON e.dept_code = d.dept_id;
子查询：
SELECT emp_name FROM employees WHERE salary > (SELECT AVG(salary) FROM employees);
SELECT emp_name FROM employees WHERE dept_code IN (SELECT dept_id FROM departments WHERE dept_name = '技术部');
SELECT emp_name FROM employees WHERE EXISTS (SELECT 1 FROM bonus_records WHERE emp_id = employees.emp_id);
事务：
START TRANSACTION;
UPDATE employees SET salary = salary * 1.1 WHERE dept_code = 2;
COMMIT;
-- 或 ROLLBACK;
用户权限：
GRANT SELECT, INSERT ON feixiang_db.* TO 'aoxiang'@'localhost';
REVOKE DELETE ON feixiang_db.* FROM 'aoxiang'@'localhost';
SHOW GRANTS FOR 'aoxiang'@'localhost';