UPDATE QUERY TAKING MORE TIME - sql-server

Question

UPDATE QUERY TAKING MORE TIME. IS THERE ANY OTHER WAY TO WRITE BELOW QUERY WITHOUT TOP 1? LIKE USING RANK OR ROWNUMBER FUNCTIONS?
SELECT proddiv,
prodstl,
prodcode,
lablcode,
proddim,
proddiv AS PRD_DIV,
prodstl AS PRD_PRODSTL,
prodcode AS PRDCOLOR,
label_code AS PRDlbl,
proddim AS par_dim,
0 AS low_level,
0 AS smuh_pkey,
IDENTITY(int) AS prdkey,
list_price
INTO #brandsdata
FROM products WITH (nolock)
DECLARE #Max INT = 30,
#x INT = 0
WHILE ( #x < 30 )
BEGIN
UPDATE t
SET smuh_pkey = (SELECT TOP 1 prdkey
FROM customers WITH (nolock)
WHERE ( proddiv = ''
OR proddiv = t.proddiv )
AND ( prodstl = ''
OR prodstl = t.prodstl )
AND ( prodcode = ''
OR prodcode = t.prodcode )
AND ( lablcode = ''
OR lablcode = t.lablcode )
AND ( proddim = ''
OR proddim = t.proddim )
AND prod_type = ''
AND active_ok = 'Y'
ORDER BY brand_name,
brand_type DESC)
FROM #brandsdata t
WHERE smuh_pkey = 0
AND low_level = #x
SET #x = #x + 1
END
THANKS IN ADVANCE.

Answer 1

Try something like this.
;with c as (
select c.prdKey, c.proddiv, c.prodstl, c.prodcode, c.lablcode, c.proddim,
ROW_NUMBER() over (
partition by c.proddiv, c.prodstl, c.prodcode, c.lablcode, c.proddim
order by c.brand_name, c.brand_type DESC) rn
from customers c
where prod_type = '' and
active_ok = 'Y'
)
update t
set smuh_pkey = c.prdKey
from #brandsdata t
inner join c
on ( c.proddiv = '' OR c.proddiv = t.proddiv )
AND ( c.prodstl = '' OR c.prodstl = t.prodstl )
AND ( c.prodcode = '' OR c.prodcode = t.prodcode )
AND ( c.lablcode = '' OR c.lablcode = t.lablcode )
AND ( c.proddim = '' OR c.proddim = t.proddim )
where c.rn = 1
I think it will not be enough for 100% of the cases, because if you can have multiple combinations of empty string with not empty, you could get different results.
then you could fine tune