What is CROSS APPLY in SQL SERVER?

Question

Aryan Kumar · Answer

Cross apply in SQL Server is a type of join that returns all possible combinations of rows from two tables. It is similar to a Cartesian product, but it is more efficient because it only returns the rows that are actually present in the tables.

The syntax for cross apply in SQL Server is as follows:

SQL

SELECT *
FROM table1
CROSS APPLY table2;

For example, the following code will return all possible combinations of rows from the Customers table and the Orders table:

SQL

SELECT *
FROM Customers
CROSS APPLY Orders;

This code will return all rows from the Customers table, even if there are no matching rows in the Orders table.

The CROSS APPLY operator is often used in conjunction with a user-defined function (UDF). For example, the following code will return all customers and their orders, where the order date is greater than today's date:

SQL

CREATE FUNCTION GetOrdersByDate(@Date DATETIME)
RETURNS TABLE
AS
BEGIN
RETURN
SELECT Customers.CustomerID, Customers.Name, Orders.OrderID, Orders.OrderDate
FROM Customers
CROSS APPLY Orders
WHERE Orders.OrderDate > @Date;
END;

The GetOrdersByDate UDF takes a date as input and returns a table with the customer ID, name, order ID, and order date for all customers who have placed an order on or after the specified date.

The CROSS APPLY operator can be a powerful tool for combining data from two or more tables. However, it is important to use it carefully, as it can also return a large number of rows.

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What is CROSS APPLY in SQL SERVER?

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