Which Test Standard has a Usage of secondary filters, and a Class of f5? Question 4
CREATE TABLE "filter_classes" (
  "usage" text,
  "class" text,
  "performance" text,
  "performance_test" text,
  "particulate_size_approaching_100pct_retention" text,
  "test_standard" text
);
SELECT "test_standard" FROM "filter_classes" WHERE "usage"='secondary filters' AND "class"='f5';