學習筆記專區

--Table Alias(別名)

select e.EMPLOYEE_ID,e.last_name,d.location_id,d.DEPARTMENT_ID--已經取了別名就不可以再寫全名了departments.DEPARTMENT_ID←(X)

from employees e join DEPARTMENTS d --employees別名e  DEPARTMENTS別名d

on e.DEPARTMENT_ID = d.DEPARTMENT_ID;

輸出結果跟沒有別名一樣

--額外條件

select e.EMPLOYEE_ID,e.last_name,d.location_id,d.DEPARTMENT_ID

from employees e join DEPARTMENTS d

on e.DEPARTMENT_ID = d.DEPARTMENT_ID--篩選條件：欄目相同

where location_id>1500--增加設定篩選條件，where不能有兩個，只有一個資料表有的欄目可以不用加別名(欄目名)(也可以加)

and d.DEPARTMENT_ID<=90--可以再用"and"再增加條件