CREATE TABLE "retina_display_models" (
  "model" text,
  "ppi_pixels_per_inch" real,
  "ppcm_pixels_per_cm" real,
  "resolution" text,
  "typical_viewing_distance_in_cm" text,
  "pixels_per_degree_ppd" real
);

Question: How many different PPI does the model with ppcm of 87 have?
SQL: SELECT COUNT("ppi_pixels_per_inch") FROM "retina_display_models" WHERE "ppcm_pixels_per_cm"=87;

Question: What's the resolution of the model with a PPD of 69?
SQL: SELECT "resolution" FROM "retina_display_models" WHERE "pixels_per_degree_ppd"=69;