SQL中的CROSS JOIN与INNER JOIN

Question

CROSS JOIN和之间有什么区别INNER JOIN？

交叉加入：

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

内部联接：

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

哪一种更好，为什么我要使用其中一种呢？

Answer 1

交叉联接不会合并行，如果每个表中有100行且1对1匹配，您将得到10.000个结果，Innerjoin在相同情况下将仅返回100行。

这两个示例将返回相同的结果：

交叉联接

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

内部联接

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

使用最后一种方法