Inge,

The others have effectively explained to you how to get around the fact that your database is not well designed. C1, C2, and C3 represent a multivalued attribute of your table and therefore are in violation of the 1st normal form. If you move the values of the 3 C fields to a related child table (named ctable) then your sql becomes;

SELECT Table1.Name, MAX(cTable.Value) ;
  FROM Table1 JOIN cTable ON Table1.ID = cTable.Id ...

Much simpler anmd faster than a seeries of IIF(0 statements in an SQL statement. This one will actually port to SQL Server or Oracle.