CREATE TABLE "structures_past_or_present_between_550_a" (
  "pinnacle_height" text,
  "year" real,
  "structure_type" text,
  "main_use" text,
  "country" text,
  "town" text
);

Question: What is the main use for the structure listed in walker city, iowa?
SQL: SELECT "main_use" FROM "structures_past_or_present_between_550_a" WHERE "town"='walker city, iowa';

Question: What year was the structure in greensboro, north carolina considered tallest?
SQL: SELECT "year" FROM "structures_past_or_present_between_550_a" WHERE "town"='greensboro, north carolina';

Question: What was the earliest year that a structure was located in gray court, south carolina?
SQL: SELECT MIN("year") FROM "structures_past_or_present_between_550_a" WHERE "town"='gray court, south carolina';

Question: What is the main use of the structure that was in redfield, arkansas before 2004?
SQL: SELECT "main_use" FROM "structures_past_or_present_between_550_a" WHERE "year"<2004 AND "town"='redfield, arkansas';