PostgreSQL is a robust and versatile relational database management system that provides several advanced features to optimize database interaction. Among these features, Functions and Stored Procedures are invaluable tools that can significantly enhance the efficiency and performance of SQL operations.

What Are PostgreSQL Functions?

Functions in PostgreSQL are named sections of SQL code that can perform operations and return a single value. They help encapsulate reusable code and logical operations, allowing for cleaner, more maintainable, and efficient database interactions.

Syntax of PostgreSQL Functions

The basic syntax for creating a function in PostgreSQL is as follows:

CREATE FUNCTION function_name(parameter_name data_type)
RETURNS return_data_type AS $$
BEGIN
    -- Body of the function
    RETURN some_value;
END;
$$ LANGUAGE plpgsql;

Example of a PostgreSQL Function

Let's create a simple function to calculate the total price of items in a sales order including tax.

CREATE FUNCTION calculate_total_price(price NUMERIC, tax_rate NUMERIC)
RETURNS NUMERIC AS $$
BEGIN
    RETURN price + (price * tax_rate);
END;
$$ LANGUAGE plpgsql;

Using the Function

You can call this function in your SQL queries like this:

SELECT calculate_total_price(100, 0.07);

This will return 107, which includes the original price and the tax.

What Are Stored Procedures?

Stored Procedures, on the other hand, are somewhat broader than functions. They are a set of SQL commands that can perform various operations (like INSERT, UPDATE, DELETE) and can return multiple values or a result set, rather than a single value.

Syntax of PostgreSQL Stored Procedures

The basic syntax for creating a stored procedure is as follows:

CREATE PROCEDURE procedure_name(parameter_name data_type)
LANGUAGE plpgsql
AS $$
BEGIN
    -- Body of the procedure
END;
$$;

Example of a PostgreSQL Stored Procedure

Here's an example of a stored procedure to add a new customer to a customer table:

CREATE PROCEDURE add_customer(name VARCHAR, email VARCHAR)
LANGUAGE plpgsql
AS $$
BEGIN
    INSERT INTO customers (name, email)
    VALUES (name, email);
END;
$$;

Calling the Stored Procedure

You can execute this procedure using the CALL statement:

CALL add_customer('John Doe', 'john.doe@example.com');

Key Differences Between Functions and Stored Procedures

1. Return Type:

   • Functions return a single value or a table.
   • Stored Procedures do not return a value but can return result sets.

2. Invocation:

   • Functions can be called from SQL statements (like SELECT).
   • Stored Procedures are called using the CALL command.

3. Purpose:

   • Functions are often used to compute and return values.
   • Stored Procedures are suited for executing complex business logic and batch processing.

When to Use Functions and Stored Procedures

Use Functions When:

• You need to compute a value based on input parameters.
• You plan to integrate the logic directly into SQL queries.
• You want to encapsulate reusable logic for reporting or calculations.

Use Stored Procedures When:

• Your logic involves multiple operations (INSERT, UPDATE) that need to happen in a sequence.
• You are performing batch jobs or chores that manipulate data without returning a specific value.
• You want to implement complex business workflows within the database.

By understanding and leveraging PostgreSQL Functions and Stored Procedures, developers can optimize their applications, abstract complex logic, and maintain cleaner codebases. Whether you are writing a simple utility function or an intricate stored procedure for data manipulation, these features are pivotal in harnessing the full capabilities of PostgreSQL.