centers machines
------- --------
center1  machine1
center2  machine2
center2  machine3

operation center1 center2 center3 ...
--------- ------- ------- ------- ...
oper1     ok       ok
oper2     ok              ok
oper3     ok

SELECT operation from dbo.operations where "center" != null

cmd.CommandText = string.Format("SELECT operation FROM dbo.Operations WHERE {0} IS NOT NULL", center);