sql server - Merge multiple rows in SQL with tie breaking on primary key -

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i have table data following

key | | b    | c ---------------------------  1  | x | 0    | 1  2  | x | 2    | 0  3  | x | null | 4  4  | y | 7    | 1  5  | y | 3    | null  6  | z | null | 4

and want merge rows based on column largest primary key being 'tie breaker' between values not null

result key | | b    | c ---------------------------  1  | x | 2    | 4  2  | y | 3    | 1  3  | z | null | 4

what best way achieve assuming data 40 columns , 1 million rows unknown level of duplications?

using row_number , conditional aggregation:

sql fiddle

with cte as(     select *,         rnb = row_number() over(partition order case when b null 0 else 1 end desc, [key] desc),         rnc = row_number() over(partition order case when c null 0 else 1 end desc, [key] desc)     tbl ) select     [key] = row_number() over(order a),     a,     b = max(case when rnb = 1 b end),     c = max(case when rnc = 1 c end) cte group

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