CREATE TABLE "fixed_focal_length_lenses" (
  "brand" text,
  "product_name" text,
  "focal_length" text,
  "35mm_efl_and_equivalent_aperture" text,
  "max_aperture" text
);

Question: What is the maximum aperture of the lens(es) with a focal length of 20mm?
SQL: SELECT "max_aperture" FROM "fixed_focal_length_lenses" WHERE "focal_length"='20mm';

Question: What is the 35mm EFL and the equivalent aperture of the lens(es) with a maximum aperture of f /2.5?
SQL: SELECT "35mm_efl_and_equivalent_aperture" FROM "fixed_focal_length_lenses" WHERE "max_aperture"='f /2.5';

Question: What is the brand of the Sigma 30mm f2.8 DN, which has a maximum aperture of f /2.8 and a focal length of 30mm?
SQL: SELECT "brand" FROM "fixed_focal_length_lenses" WHERE "max_aperture"='f /2.8' AND "focal_length"='30mm' AND "product_name"='sigma 30mm f2.8 dn';