When should I use CROSS APPLY over INNER JOIN?

Question

Aryan Kumar · Answer

Cross apply and inner join are both SQL join clauses that are used to combine data from two or more tables. However, they have different purposes and should be used in different situations.

Cross apply is used to create a Cartesian product of two tables. This means that it will return all possible combinations of rows from the two tables, even if there is no matching row in the other table.

Inner join is used to join two tables based on a common value. This means that it will only return rows from the two tables where there is a matching row in the other table.

In general, you should use cross apply when you want to return all possible combinations of rows from two tables. For example, you might use cross apply to get a list of all possible orders that could be made from a list of products and a list of customers.

You should use inner join when you want to return only the rows that match between two tables. For example, you might use inner join to get a list of all orders that were made by a specific customer.

Here is a table that summarizes the differences between cross apply and inner join:

Feature	Cross apply	Inner join
Creates a Cartesian product	Yes	No
Returns all possible combinations of rows	Yes	No
Returns only matching rows	No	Yes
When to use	When you want to return all possible combinations of rows	When you want to return only matching rows

Here is an example of how to use cross apply:

SQL

SELECT *
FROM Customers
CROSS APPLY Orders;

This code will return all possible combinations of rows from the Customers table and the Orders table. This means that it will return all rows from the Customers table, even if there are no matching rows in the Orders table.

Here is an example of how to use inner join:

SQL

SELECT *
FROM Customers
INNER JOIN Orders
ON Customers.CustomerID = Orders.CustomerID;

This code will return only the rows from the Customers table that have a matching row in the Orders table. This means that it will only return rows from the Customers table where there is a corresponding order in the Orders table.

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When should I use CROSS APPLY over INNER JOIN?

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