DELIMITER //
CREATE PROCEDURE test()
BEGIN
DECLARE first_invoice_due_date DATE;
SELECT MIN(invoice_due_date)
INTO first_invoice_due_date
FROM invoices
WHERE invoice_total - payment_total - credit_total > 0;
IF first_invoice_due_date < NOW() THEN
SELECT 'Outstanding invoices are overdue!';
ELSEIF first_invoice_due_date = NOW() THEN
SELECT 'Outstanding invoices are due today!';
ELSE
SELECT 'No invoices are overdue.';
END IF;
END//
While this does show how a IF statement can be used, the procedure itself does not make much sense
Why only look at 1 invoice