Question

One of the columns in my table is “DataSource”. Datasource can have two values, lets say “A” or “B”. I would like to always take the row when Datasource = “A”, however, if there isn’t an entry for A I would like to take “B”.

How does one do this in SQL Server?

EDIT:

So for a partucular product (Product ID) one Product ID may have two rows, each containing a different DataSource, wheres another ProductID may only have one DataSource:

{ProductID DataSource}
{1  A},
{1  B},
{2  B}

Here I would wish to select the top and bottom row

Answer 1

Based on your sample data, this works:

SELECT ProductID, MIN(DataSource)
FROM @tab
GROUP BY ProductID;

And here is my test data:

declare @tab table (ProductID int, DataSource char(1))
insert into @tab values (1, 'A');
insert into @tab values (1, 'B');
insert into @tab values (2, 'B');

If there are more columns in the table than the two you show then:

SELECT T1.*
FROM @tab T1
JOIN
(
    SELECT ProductID, MIN(DataSource) AS DataSource
    FROM @tab
    GROUP BY ProductID
) T2 ON T1.ProductID = T2.ProductID AND T1.DataSource  = T2.DataSource