DB

(1)(2)(3)效果一样

(1) where

SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo
FROM Persons, Orders
WHERE Persons.Id_P = Orders.Id_P

(2)inner join

SELECT column_name(s)
FROM table1
INNER JOIN table2
ON table1.column_name=table2.column_name;

(3)join

SELECT column_name(s)
FROM table1
JOIN table2
ON table1.column_name=table2.column_name;

all kinds of join

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