一、語法

select 查詢列表
from 表
where 篩選條件
order by 排序列表 [asc/desc]

特點：

SELECT * FROM employees ORDER BY salary DESC;

SELECT *
FROM employees
 
WHERE department_id>=90 
ORDER BY employee_id DESC;

注意： 排序 order by前面不需寫 邏輯符 連線，否則會報錯。

#3、按表示式排序
#案例：查詢員工資訊 按年薪降序

SELECT *,salary*12*(1+IFNULL(commission_pct,0))
FROM employees
ORDER BY salary*12*(1+IFNULL(commission_pct,0)) DESC;

#4、按別名排序
#案例：查詢員工資訊 按年薪升序

SELECT *,salary*12*(1+IFNULL(commission_pct,0
 
)) 年薪
FROM employees
ORDER BY 年薪 ASC;     //order by 後面支援別名

#5、按函式排序
#案例：查詢員工名，並且按名字的長度降序

SELECT LENGTH(last_name),last_name 
FROM employees
ORDER BY LENGTH(last_name) DESC;

SELECT *
FROM employees
ORDER BY salary DESC,employee_id ASC;

測試：查詢郵箱中包含e的員工資訊，並先按郵箱的位元組數降序，再按部門號升序

SELECT *,LENGTH(email)
FROM employees
WHERE email LIKE '%e%'                            
ORDER BY LENGTH(email) DESC,department_id ASC;  #包含寫法: '% 字元 %'