**order by 可以 放 单个字段 可以放多个字段 表达式 函数 别名 order by 一般 放在查询的最后 但是limit 在最后**
SELECT * FROM employees ORDER BY salary DESC;
SELECT * FROM employees ORDER BY salary ASC;
SELECT * FROM employees WHERE department_id >=90 ORDER BY hiredate ;
SELECT
*,
salary * 12 * (1+ IFNULL (commission_pct, 0)) "年薪"
FROM
employees
ORDER BY "年薪" DESC;
SELECT LENGTH ('JOHN');
SELECT LENGTH(last_name) len ,last_name, salary FROM employees ORDER BY LENGTH(last_name);
SELECT * FROM employees ORDER BY salary ASC,employee_id DESC;
SELECT last_name "姓名" ,salary FROM employees WHERE salary NOT BETWEEN 10000 AND 17000 ORDER BY salary DESC;