T-SQL Experts Please Correct Me !

Here is the original script
select count(*) FROM (select * from aecprda where
AECPRDA.sales_cat_cd in ('02','10') and
(create_dt > '2008-02-17 18:10:22.000' or price_chg_dt > '2008-02-17 18:10:22.000')
) AS AECPRDA_1
left join (zfmt z inner join muzealbums on z.muzenbr=muzealbums.muzenbr) on AECPRDA_1.product_id = z.vendorcode
and z.Vendorname = N'Alliance'
LEFT OUTER JOIN AECMCAT aecmcat_c3
ON AECPRDA_1.mcat_cd3 = aecmcat_c3.Mcat_cd

I want to add a condition [(substring(AECPRDA_1.upc_1,1,11) = substring(z.upc,1,11) or
(AECPRDA_1.product_id = z.vendorcode))] instead of [AECPRDA_1.product_id = z.vendorcode] TO THE ABOVE STATEMENT.
It is a secondary match condition

1. If aecprda_1.upc_1 doesn€™t find a match on zfmt.upc then
2. Match on aecprda_1. product_id = zfmt. Vendorcode
3. I also want to add a condition if there is a product match on both 1 & 2 , then take only the first one and don€™t take the second one.

Something looks like below statement but needs one more condition mentioned at item 3 to be added.

select count(*) FROM (select * from aecprda where
AECPRDA.sales_cat_cd in ('02','10') and
(create_dt > '2007-10-22 00:00:00.000' or price_chg_dt > '2007-10-22 00:00:00.000')
) AS AECPRDA_1
left join (zfmt z inner join muzealbums on z.muzenbr=muzealbums.muzenbr) on (substring(AECPRDA_1.upc_1,1,11) = substring(z.upc,1,11) or
(AECPRDA_1.product_id = z.vendorcode))
and z.Vendorname = N'Alliance'
LEFT OUTER JOIN AECMCAT aecmcat_c3
ON AECPRDA_1.mcat_cd3 = aecmcat_c3.Mcat_cd --- I ran this query executing takes hour eventhough appropriate indices were added.

Any help is greatly appreciated.