sql server - design deduplication sql statement using NULLS vs MAX VALUE -


i'm trying sculpt sql statement de-dupicate table.

the table has 3 keys: key1, key2, key3 used business key. date being used.

the rules (assuming matches in key1, key2, key3):

if rows have dates, retain max(date) if 1 row has date, , others null, retain row date if rows has date = null, keep rows.

i've been using code basis:

with cte as(    select [key1], [key2], [key3], [date],        rn = row_number()over(partition [key1], [key2], [key3], [date] order [date] desc)    dbo.table1 ) delete cte rn > 1

i not educated on how apply rules on sql statement. wisdom appreciated.

example deduplications:

case 1: before dedupication:             key1    key2    key3    date 1     1   null 1     1   null 1     1   null  after deduplication:             key1    key2    key3    date 1     1   null 1     1   null 1     1   null  case 2: before dedupication:             key1    key2    key3    date 1     1   1/1/2016 1     1   1/1/2016 1     1   1/1/2016  after deduplication:             key1    key2    key3    date 1     1   1/1/2016  case 3: before dedupication:             key1    key2    key3    date 1     1   1/1/2016 1     1   1/2/2016 1     1   1/3/2016  after deduplication:             key1    key2    key3    date 1     1   1/3/2016  case 4: before deduplication             1     1   1/1/2016 1     1   1/1/2016 1     1   null  after deduplication:             key1    key2    key3    date 1     1   1/1/2016   case 5: before deduplication             1     1   1/1/2016 1     1   1/2/2016 1     1   null  after deduplication:             key1    key2    key3    date 1     1   1/2/2016 

with cte as(    select [key1], [key2], [key3], [date],        rn = row_number() on (partition [key1], [key2], [key3] order [date] desc),        mxd = max([date]) on (partition [key1], [key2], [key3])    dbo.table1 ) delete cte rn > 1 , mxd not null

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