排序
SELECT employee_id, first_name, last_name, hire_date, salary
FROM employees
ORDER BY first_name;
ORDER BY hire_date ASC;
ORDER BY hire_date DESC;
SELECT employee_id, first_name, last_name, hire_date, salary
FROM employees
ORDER BY first_name, last_name DESC
![在这里插入图片描述](https://img-blog.csdnimg.cn/f48cc5a02030455fbba56479867cd7e7.png)
![在这里插入图片描述](https://img-blog.csdnimg.cn/2968feb5cec249ceacefb19c07d2c976.png)
SELECT employee_id, first_name, last_name, hire_date, salary
FROM employees
ORDER BY 2, 3 DESC
SELECT employee_id, manager_id
FROM employees
ORDER BY manager_id DESC;
SELECT employee_id, manager_id
FROM employees
ORDER BY manager_id NULLS FIRST;
返回top
SELECT first_name, last_name, salary
FROM employees
ORDER BY salary
LIMIT 10;
![在这里插入图片描述](https://img-blog.csdnimg.cn/eba5df1534d74a0c829d4cef55a7582e.png)
SELECT first_name, last_name, salary
FROM employees
ORDER BY salary
FETCH FIRST 10 ROWS WITH TIES;
![在这里插入图片描述](https://img-blog.csdnimg.cn/93270fb09de34e7fb498973a987d7cd0.png)
SELECT first_name, last_name, salary
FROM employees
ORDER BY salary
OFFSET 10 ROWS
FETCH FIRST 10 ROWS ONLY;
SELECT first_name, last_name, salary
FROM employees
ORDER BY salary
LIMIT 10 OFFSET 10;
条件表达case
SELECT first_name, last_name,
CASE
WHEN salary <5000 THEN '低收入'
WHEN salary between 5000 and 100000 THEN '中等收入'
ELSE '高收入'
END AS "收入等级"
FROM employees;
![在这里插入图片描述](https://img-blog.csdnimg.cn/c8d389ca827c46139008ab75e3948b7b.png)
SELECT COUNT(CASE department_id WHEN 10 THEN 1 END) dep_cnt_10,
COUNT(CASE department_id WHEN 20 THEN 1 END) dep_cnt_20,
COUNT(CASE department_id WHEN 30 THEN 1 END) dep_cnt_30
FROM employees;
![在这里插入图片描述](https://img-blog.csdnimg.cn/2b127273fc03452ab0b1110eeb05a266.png)