Which  Performance has a Test Standard of bs en779, and a Particulate size approaching 100% retention of >2µm, and a Class of f6?
CREATE TABLE "filter_classes" (
  "usage" text,
  "class" text,
  "performance" text,
  "performance_test" text,
  "particulate_size_approaching_100pct_retention" text,
  "test_standard" text
);
SELECT "performance" FROM "filter_classes" WHERE "test_standard"='bs en779' AND "particulate_size_approaching_100pct_retention"='>2µm' AND "class"='f6';