Question

I have a table:

Type (PK)         Year (PK)    Value
Default           2000         1
Default           2001         2
UserFooAdjusted   2001         3
UserBarAdjusted   2001         4

What is the fastest SQL query that returns distinct years and if there are two rows with the same year then the user adjusted value is returned? There are multiple users. The query returns data for one user. Example result:

Year    Value
2000    1
2001    3

I’ve thougt about A UNION B but how do I always keep the duplicate from B? Maybe a better solution would be to divide the current table into two tables: one would contain default values and the other would contain user adjusted vaules?

Answer 1

Assuming that there are only two types: Default and UserAdjusted, you can use Common Table Expression and Window Functions, in sql server.

WITH recordList
AS
(
    SELECT   YEAR, VALUE,
             ROW_NUMBER() OVER (PARTITION BY  YEAR
                                ORDER BY TYPE DESC) rn
    FROM    tableName
)
SELECT  YEAR, VALUE
FROM    recordList
WHERE   rn = 1

• SQLFiddle Demo