Select first field from column in group value

Question

Hello,
I need to return the first row of data grouped by the first field (Visit ID) in multi-column table:
VisitID       AdmitDate            Unit       Room          OrderCode
001041      2014-08-01         2E          202            SWCC
001041      2014-08-01         2E          202            NULL
006811      2014-08-01         2E          204            SWCC
008815      2014-08-01         2E          206            NULL
004895      2014-08-01         2E          207            SWFA
004895      2014-08-01         2E          207            SWCC
004895      2014-08-01         2E          207            NULL
To return:
001041      2014-08-01         2E          202            SWCC
006811      2014-08-01         2E          204            SWCC
008815      2014-08-01         2E          206            NULL
004895      2014-08-01         2E          207            SWFA
I currently have a group by clause with all field names; and have tried max on the OrderCode in the select that doesn't work, and FIRST isn't recognized in SSL server.  Do I need a subquery (if so, how as I'm newer to writing SQL) or what is another
solution?  Thank you.

Answer 1

create table t (VisitID varchar(50), AdmitDate date, Unit varchar(50),Room varchar(50),OrderCode varchar(50))
insert into t values ('001041' , '2014-08-01' , '2E' , 202 , 'SWCC' ),
('001041', '2014-08-01' , '2E' , 202 , NULL),
('006811' , '2014-08-01' , '2E' , 204 , 'SWCC'),
('008815' , '2014-08-01' , '2E' , 206 , NULL),
('004895' , '2014-08-01' , '2E' , 207 , 'SWFA'),
('004895' , '2014-08-01' , '2E' , 207 , 'SWCC'),
('004895' , '2014-08-01' , '2E' , 207 , NULL)
--To return:
--001041 2014-08-01 2E 202 'SWCC'
--006811 2014-08-01 2E 204 'SWCC'
--008815 2014-08-01 2E 206 NULL
--004895 2014-08-01 2E 207 'SWFA'
select VisitID,AdmitDate,Unit,Room , max(OrderCode) as OrderCode from t
group by VisitID,AdmitDate,Unit,Room
Order by VisitID
--Or
select VisitID,AdmitDate,Unit,Room ,OrderCode from (
select VisitID,AdmitDate,Unit,Room ,OrderCode, Row_number() Over(Partition By VisitID Order by OrderCode DESC) rn from t
)t
WHERE rn=1
Order by VisitID
drop table t