How do I put an 'if clause' in an SQL string?

Question

So here\'s what I want to do on my MySQL database.

I would like to do:

SELECT *
    FROM itemsOrdered
    WHERE purchaseOrder_ID = \'@purchaseOr         


        

Answer 1

If the table contains millions of records then the following query will work fast.

UPDATE PO
SET PO.purchaseOrder_status = 'COMPLETED'
FROM purchaseOrder PO
LEFT OUTER JOIN itemsOrdered IOD ON IOD.purchaseOrder_ID = PO.purchaseOrdered_ID and IOD.status = 'PENDING'
WHERE IOD.purchaseOrder_ID IS NULL