Table: tallest_structures_2
Columns: pinnacle_height
year
structure_type
main_use
country
town

Question: What is the main use for the structure listed in walker city, iowa?
SQL: SELECT "main_use" FROM tallest_structures_2 WHERE "town" = 'walker city, iowa'

Question: What year was the structure in greensboro, north carolina considered tallest?
SQL: SELECT "year" FROM tallest_structures_2 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 tallest_structures_2 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 tallest_structures_2 WHERE "year" < 2004 AND "town" = 'redfield, arkansas'