AS
SELECT column_name(s)
FROM table_name
AS alias_name
SELECT column_name AS alias_name
FROM table_name
SELECT po.OrderID, p.LastName, p.FirstName
FROM Persons AS p, Product_Orders AS po
WHERE p.LastName='Adams' AND p.FirstName='John'
SELECT LastName AS Family, FirstName AS Name
FROM Persons
KEY
- 主鍵(Primary Key)是一個列,在這個列中的每一行的值都是唯一的。在表中,每個主鍵的值都是唯一的。這樣做的目的是在不重複每個表中的所有數據的情況下,把表間的數據交叉捆綁在一起
SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo
FROM Persons, Orders
WHERE Persons.Id_P = Orders.Id_P
JOIN
- INNER JOIN 表中存在至少一個匹配時返回行
SELECT column_name(s)
FROM table_name1
INNER JOIN table_name2
ON table_name1.column_name=table_name2.column_name
SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo
FROM Persons
INNER JOIN Orders
ON Persons.Id_P = Orders.Id_P
ORDER BY Persons.LastName
- LEFT JOIN 即使右表中沒有匹配,也從左表返回所有的行
SELECT column_name(s)
FROM table_name1
LEFT JOIN table_name2
ON table_name1.column_name=table_name2.column_name
SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo
FROM Persons
LEFT JOIN Orders
ON Persons.Id_P=Orders.Id_P
ORDER BY Persons.LastName
- RIGHT JOIN 即使左表中沒有匹配,也從右表返回所有的行
- FULL JOIN 只要其中一個表中存在匹配,就返回行