Joining mysql tables
Plain  JOIN a,b generate the cartesian product where each row from a is combined with each row of b, despite of related they are or no. There are not only duplicates for certain user but also the rows for PCs not related to the certain user. If you restrict the output by DISTINCT there is no guarantee you'll get the proper row from the cartesian set. You have to JOIN .. ON by some column but you have to provide your tables structure for further analysis.