DAYNAME problem using CASE statement

[John Noble]

Hi folks,

Im having difficulty in determining the dayname on a stored proc.
Here is my proc.

CREATE DEFINER=`root`@`%` PROCEDURE `usp_SalesHistoryFrenchTransportDocsTest`(
IN p_despatchDate date
)
BEGIN

SELECT CASE salesHistory.despatchDate WHEN DAYNAME(p_despatchDate) = "Saturday" THEN
DATE_ADD(salesHistory.despatchDate, INTERVAL 2 DAY)
ELSE
DATE_ADD(salesHistory.despatchDate, INTERVAL 1 DAY) END as despatchDate FROM salesHistory
WHERE saleshistory.despatchDate = p_despatchDate;


END

When I use call usp_SalesHistoryFrenchTransportDocsTest('2020-04-04') (which is a Saturday), I expect the data to add 2 days on to it. But it always adds 1 day. It does not seem to to be catching on the first case statement.

What am I missing here?

J