Looking for the best way to return pass in a parameter to allow me to return a specific customer or all customers in SQL - sql

Question

I have the below query that could defenitely be optimized but I'm looking for the best way to add a parameter that allows me to return the same results and pass in a Parameter that would say if pass it in as "All" it would return all WO.BillTo records but if I passed in a value other than "All" it would compare that value to the WO.BillTo to only return records for that specific BillTo Customer.
Any help or suggestions would be greatly appreciated.
SELECT WO.WONo ,
WO.BillTo ,
WO.ShipTo ,
WO.ShipName ,
WO.ClosedDate ,
WOParts.PartNo ,
WOParts.Description ,
WOParts.ShipQty ,
WOParts.SellRate ,
Customer.Name
FROM WO,WOParts,Customer
WHERE (((
((WO.ClosedDate >= #startdate ) AND (WO.ClosedDate < #closedate ) )
AND (WO.Disposition = 2 ) )
AND (WO.WONo = WOParts.WONo ) )
AND (WO.BillTo = Customer.Number ) )
AND WOParts.TransferWONoTo =''
and Woparts.shipqty <> 0
order by wo.ShipTo

Answer 1

This is known as a "catch all" query. I would suggest using NULL rather than 'all', but the syntax would be the same. The OPTION (RECOMPILE) is there to stop poor query plan caching. Also I've "updated" you to 1992's ANSI-92 explicit JOIN syntax, as it has been around for around 30 years now:
SELECT W.WONo ,
W.BillTo ,
W.ShipTo ,
W.ShipName ,
W.ClosedDate ,
WP.PartNo ,
WP.Description ,
WP.ShipQty ,
WP.SellRate ,
C.Name
FROM dbo.WO W --Let's update to 1992!
JOIN dbo.WOParts WP ON W.WONo = WP.WONo
JOIN dbo.Customer C ON W.BillTo = C.Number
WHERE W.ClosedDate >= #startdate AND W.ClosedDate < #closedate
AND W.Disposition = 2
AND WP.TransferWONoTo =''
AND WP.shipqty <> 0
AND (WO.BillTo = #YourParameter OR #YourParameter IS NULL)
ORDER BY W.ShipTo
OPTION (RECOMPILE);