How to Use CROSS APPLY with Table-Valued Functions in SQL

Use CROSS APPLY with Table-Valued Functions

Write a SQL query to join a table with a table-valued function using CROSS APPLY.

Solution:

-- Join a table with a table-valued function using CROSS APPLY.
SELECT 
    E.EmployeeID,
    E.Name,
    D.DepartmentName
FROM Employees E
CROSS APPLY GetDepartmentDetails(E.DepartmentID) AS D;

Explanation:

1. Purpose of the Query :

1. The goal is to demonstrate how to use CROSS APPLY to invoke a table-valued function (GetDepartmentDetails) for each row in the Employees table.

2. Key Components :

1. CROSS APPLY : Joins the main table (Employees) with the result set returned by the table-valued function.
2. GetDepartmentDetails(E.DepartmentID) : A table-valued function that retrieves department details.

3. Why use CROSS APPLY? :

1. CROSS APPLY is useful when you need to apply a function to each row of a table and include its results in the query.

4. Real-World Application :

1. For example, in organizational databases, you might use this query to retrieve department details for each employee dynamically.

Additional Notes:

• CROSS APPLY filters out rows where the function returns no results.
• Use this exercise to teach how to integrate table-valued functions into queries.

For more Practice: Solve these Related Problems:

• Write a SQL query to join a products table with a table-valued function that calculates discounts.
• Write a SQL query to retrieve detailed order information for each customer using CROSS APPLY.
• Write a SQL query to apply a custom function to each row in a sales table to compute bonuses.
• Write a SQL query to fetch related documents for each user using a table-valued function.

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