SQL 中的 CROSS JOIN 与 INNER JOIN [英] CROSS JOIN vs INNER JOIN in SQL

问题描述

CROSS JOIN 和 INNER JOIN 有什么区别?

交叉连接:

SELECT 
    Movies.CustomerID, Movies.Movie, Customers.Age, 
    Customers.Gender, Customers.[Education Level], 
    Customers.[Internet Connection], Customers.[Marital Status], 
FROM   
    Customers 
CROSS JOIN 
    Movies

内连接:

SELECT 
    Movies.CustomerID, Movies.Movie, Customers.Age, 
    Customers.Gender, Customers.[Education Level], 
    Customers.[Internet Connection], Customers.[Marital Status]
FROM   
    Customers 
INNER JOIN 
    Movies ON Customers.CustomerID = Movies.CustomerID

哪一个更好，为什么我要使用任何一个?

Which one is better and why would I use either one?

推荐答案

Cross join 不合并行，如果每个表中有 100 行且 1 比 1 匹配，则得到 10.000 个结果，Innerjoin 只会返回 100 行在同样的情况下.

Cross join does not combine the rows, if you have 100 rows in each table with 1 to 1 match, you get 10.000 results, Innerjoin will only return 100 rows in the same situation.

这两个示例将返回相同的结果:

These 2 examples will return the same result:

交叉连接

select * from table1 cross join table2 where table1.id = table2.fk_id

内连接

select * from table1 join table2 on table1.id = table2.fk_id

使用最后一种方法

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