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Creating user-defined functions in SQL CLI

In SQL, user-defined functions (UDFs) allow you to encapsulate reusable logic and perform calculations, transformations, or validations within your queries. In this blog post, we will explore the process of creating user-defined functions in SQL CLI (Command Line Interface).

Table of Contents

What is a User-Defined Function

A user-defined function (UDF) is a defined set of SQL code that can be invoked and used in SQL queries. It allows you to modularize your code and reuse it across different parts of your queries, making them more organized and easier to maintain.

Creating User-Defined Functions in SQL CLI

To create a user-defined function in SQL CLI, you need to follow these steps:

  1. Connect to your database using the SQL CLI.
  2. Use the CREATE FUNCTION statement to define the function name, input parameters, return type, and the logic inside the function.
  3. Write the SQL code inside the function body.
  4. Use the RETURN statement to specify the value to be returned by the function.
  5. Save the function.

Here is the syntax for creating a user-defined function in SQL CLI:

CREATE FUNCTION function_name([parameter1 datatype1[, parameter2 datatype2[, ...]]])
  RETURNS return_datatype
  [LANGUAGE {SQL | language_name}]
  [DETERMINISTIC]
  [COMMENT 'string']
  BEGIN
    -- Function body
    -- SQL code goes here
  END

Let’s explore this with an example in the next section.

Examples

Let’s create a simple user-defined function that returns the total price of a product by multiplying the unit price with the quantity. Assume we have a table named products with columns id, name, unit_price, and quantity.

CREATE FUNCTION calculate_total_price(unit_price decimal(10,2), quantity int)
  RETURNS decimal(10,2)
  BEGIN
    DECLARE total_price decimal(10,2);
    SET total_price = unit_price * quantity;
    RETURN total_price;
  END

In the above example, we defined a function calculate_total_price that takes unit_price and quantity as input parameters and returns the total price as decimal(10,2). Inside the function body, we declared a variable total_price, calculated the total price by multiplying unit_price with quantity, and then returned the calculated total price using the RETURN statement.

Now, we can use this user-defined function in our SQL queries:

SELECT name, calculate_total_price(unit_price, quantity) AS total_price
FROM products;

This will give us the name of the product and its total price.

Conclusion

In this blog post, we learned about user-defined functions (UDFs) in SQL CLI and how to create them. UDFs help in encapsulating reusable logic and making SQL queries more modular and readable. By creating user-defined functions, you can reduce code repetition and improve code maintainability.

Try incorporating user-defined functions in your SQL CLI workflow, and you’ll see how it enhances your query development experience.

Happy coding! 🚀

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