display premium only for distinct row

To achieve your requirement in SQL Server, you can use a combination of ROW_NUMBER() function and a CASE statement to conditionally display the premium values based on the effdate and policynumber columns.

Here's an example query that should achieve your requirement:

SELECT policynumber, effdate,
  CASE
    -- Display premium value only for the first row
    WHEN ROW_NUMBER() OVER (PARTITION BY policynumber, effdate ORDER BY losstype) = 1
      THEN premium
    -- Display zero for all other rows with the same effdate and policynumber
    ELSE 0
  END AS premium,
  losstype
FROM lossrun