SELECT Main_Query.field_a, Main_Query.field_b, Main_Query.field_c, Main_Query.dates, [P1 testing].DRV, [P2 testing].PASS
FROM (Main_Query LEFT JOIN [P1 testing] ON Main_Query.dates = [P1 testing].Dates) LEFT JOIN [P2 testing] ON Main_Query.dates = [P2 testing].Dates;