PL/SQL: Conditional Where - asp.net

Question

I have the following scenario:
CREATE OR REPLACE PROCEDURE GETINBOX
(
inHasAttachments IN int
)
AS
BEGIN
SELECT M.MailId,
M.SenderId,
E.Emp_Name As "Sender",
MI.RecipientId,
M.Subject
FROM MAIL M INNER JOIN MAILINBOX MI ON M.MailId = MI.MailId
WHERE MI.RecipientId = '547' AND
M.NotificationSelected = 'Y'
IF inHasAttachments = '1' THEN
AND M.Attachments = 'Y'
END IF;
END GETINBOX;
Is it possible to add conditions to the where clause based on the value of a parameter?
WHERE MI.RecipientId = '547' AND
M.NotificationSelected = 'Y'
IF inHasAttachments = '1' THEN
AND M.Attachments = 'Y'
END IF;
Obviously this is not allowed but is it possible to do this in some way in PL/SQL?
I know one way to do it is to duplicate the query and execute a different query based on the value of the parameter but I don't want to duplicate my code.

Answer 1

As I understand your requirements: if the value of parameter inHasAttachments is 1 then you want to filter further by M.Attachments = 'Y', and if its value isn't 1 then you don't care about M.Attachments. This is in addition to the condition MI.RecipientId = '547' AND M.NotificationSelected = 'Y'.
You can do it like this:
SELECT M.MailId,
M.SenderId,
E.Emp_Name As "Sender",
MI.RecipientId,
M.Subject
FROM MAIL M INNER JOIN MAILINBOX MI ON M.MailId = MI.MailId
WHERE MI.RecipientId = '547' AND M.NotificationSelected = 'Y'
AND (inHasAttachments <> '1' OR M.Attachments = 'Y')