IF Cell Blank Move on to Next If Statment Or Query Version

Basically, i Have 5 Cells, with a drop down list of names. So your name may show up on a list in either cell A;E But never more then once. So basically i have a query Statement saying =QUERY(Responses!$A$2:$AL, "Select A,T,E,AB,V,W,AC where AB is not null") I need to find a way that searches If C2:C is not blank then do above query, if it's blank then move on to Cell D2:D with a Slightly Different Query ^ etc. http://ift.tt/1Y7ZWMZ So in S.W.A.T. Tab, im using the above query statement to check if AB is not empty it will display the list of items, problem being "E" is a possible list of names but so is C,I,K,M on the "responses" Sheet. I've made a "Example sheet" which outlines what im looking for.