[MonetDB-users] Clustered Index and Merge Join

I have two tables of the form R1(x INTEGER, y INTEGER) R2(x INTEGER, y INTEGER) where x and y both are NOT NULL and may both contain duplicate values (however, the combination (a,b) is unique). My questions are the following: a.) Is there a possibility to create a /clustered/ index on the x-column (or a clustered combined x-y index?). I could also create a PRIMARY KEY on (x,y). Would this result in a clustered index? Is there any command to find out which indices are clustered? b.) Does MonetDB support MergeJoins? I.e., assume I have a clustered index on columns R1.a and R2.a and perform a join on these columns, will this join be realized by an efficient merge join? Best regards, Michael