[Solved] SELECT statement with if ELSE in SQL Server

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If I understood your question correctly, you want distinct ref number with doc number is the following condition (as per the output shown).
If the all the existing doc numbers are same for a ref number, then get max(doc) otherwise sum(doc).

SELECT  ref,
        (CASE WHEN MAX(doc) = MIN(doc) THEN MAX(doc) ELSE SUM(doc) END) AS doc
FROM    table1
GROUP BY ref

solved SELECT statement with if ELSE in SQL Server