How to return values for stored procedure in postgresql?

If you’re working with stored procedures in PostgreSQL and need to return values, here’s how you can do it:

1. Understanding Stored Procedures vs. Functions

In PostgreSQL, a stored procedure (CALL procedure_name()) does not return values directly.

If you need to return values, you should either:

•  Use OUT parameters in a procedure.
  
•  Use a function (SELECT function_name()), which can return a value or table.
  

2. Using OUT Parameters in a Stored Procedure

If you need to return multiple values, use OUT parameters:

CREATE PROCEDURE get_user_details(IN user_id INT, OUT username TEXT, OUT email TEXT)
LANGUAGE plpgsql
AS $$
BEGIN
    SELECT name, email INTO username, email FROM users WHERE id = user_id;
END;
$$;

Calling the procedure:

  CALL get_user_details(1, NULL, NULL);

OUT parameters will hold the returned values.

3. Using a FUNCTION Instead (Preferred for Returning Values)

If you need a single return value or a table, use a function instead:

CREATE FUNCTION get_user_email(user_id INT) RETURNS TEXT AS $$
DECLARE email TEXT;
BEGIN
    SELECT users.email INTO email FROM users WHERE id = user_id;
    RETURN email;
END;
$$ LANGUAGE plpgsql;

Calling the function:

  SELECT get_user_email(1);

 Functions can be used in SELECT queries, unlike procedures.

4. Key Takeaways

•  Stored procedures don’t return values directly—use OUT parameters.
  
•   Use functions (RETURNS) if you need to return a value or table.
  
•   Functions can be used in SELECT statements, making them more flexible.
  

In PostgreSQL, you can return values from a stored procedure using the RETURN statement. Here's an example of how to define and return values from a stored procedure:

CREATE OR REPLACE FUNCTION get_employee_salary(employee_id INT)
RETURNS INT  -- Define the return type
AS $$
DECLARE
    salary INT;
BEGIN
    -- Retrieve the salary for the given employee_id
    SELECT emp_salary INTO salary
    FROM employees
    WHERE emp_id = employee_id;
    -- Return the salary
    RETURN salary;
END;
$$ LANGUAGE plpgsql;

In this example:

• We create a stored procedure named get_employee_salary.
  
• The procedure takes one parameter, employee_id, and returns an integer value (the employee's salary).
  
• Within the procedure, we declare a local variable salary to store the retrieved salary value.
  
• We use a SELECT INTO statement to fetch the salary for the given employee_id from the employees table and store it in the salary variable.
  
• Finally, we use the RETURN statement to return the value of salary.

To call this stored procedure and retrieve the returned value, you can use a SQL query like this:

SELECT get_employee_salary(123);

This will execute the stored procedure and return the salary value for the specified employee. If you're executing the procedure from within another PL/pgSQL block or function, you can also capture the returned value using variables.