Eliminating duplicate rows except one column with condition - sql

Question

I am having trouble trying to find an appropriate query(SQL-SERVER) for selecting records with condition however, the table I will be using has more than 100,000 rows and more than 20 columns.
So I need a code that satisfies the following condition:
1.)If [policy] and [plan] column is unique between rows then I will select that record
2.)If [policy] and [plan] return 2 or more rows then I will select the record which 'code' column isn't 999
3.)In some cases the unwanted rows may not have '999' in [code] column but may be other specifics
In other words, I would like to get row number 1,2,4,5,7.
Here is an example of what the table looks like
row #|policy|plan|code
-----------------------
1 | a | aa |111
-----------------------
2 | b | bb |112
-----------------------
3 | b | bb |999
-----------------------
4 | c | cc |111
-----------------------
5 | c | cc |112
-----------------------
6 | c | cc |999
-----------------------
7 | d | dd |999
-----------------------
I'm expecting to see something like
row #|policy|plan|code
-----------------------
1 | a | aa |111
-----------------------
2 | b | bb |112
-----------------------
4 | c | cc |111
-----------------------
5 | c | cc |112
-----------------------
7 | d | dd |999
-----------------------
Thank you in advance

Answer 1

This sounds like a prioritization query. You an use row_number():
select t.*
from (select t.*,
row_number() over (partition by policy, plan
order by code
) as seqnum
from t
) t
where seqnum = 1;
The expected output makes this a bit clearer:
select t.*
from (select t.*,
rank() over (partition by policy, plan
order by (case when code = 999 then 1 else 2 end) desc
) as seqnum
from t
) t
where seqnum = 1;
The OP wants all codes that are not 999 unless the only codes are 999. So, another approach is:
select t.*
from t
where t.code <> 999
union all
select t.*
from t
where t.code = 999 and
not exists (select 1
from t t2
where t2.policy = t.policy and t2.plan = t.plan and
t2.code <> 999
);

Answer 2

May be you want this (eliminate the last row if more than one)?
select t.*
from (select t.*
, row_number() over (partition by policy, plan
order by code desc
) AS RN
, COUNT(*) over (partition by policy, plan) AS RC
from t
) t
where RN > 1 OR RN=RC;
Output:
row policy plan code RN RC
1 1 a aa 111 1 1
2 2 b bb 112 2 2
3 5 c cc 112 2 3
4 4 c cc 111 3 3
5 7 d dd 999 1 1

Answer 3

CREATE TABLE #Table2
([row] int, [policy] varchar(1), [plan] varchar(2), [code] int)
;
INSERT INTO #Table2
([row], [policy], [plan], [code])
VALUES
(1, 'a', 'aa', 111),
(2, 'b', 'bb', 112),
(3, 'b', 'bb', 999),
(4, 'c', 'cc', 111),
(5, 'c', 'cc', 112),
(6, 'c', 'cc', 999),
(7, 'd', 'dd', 999)
;
with cte
as
(
select *,
row_number() over (partition by policy, [plan]
order by code
) as seqnum
from #Table2
)
select [row], [policy], [plan], [code] from cte where seqnum=1