CREATE TABLE table_name_15 (school VARCHAR2, year_joined VARCHAR2, year_left VARCHAR2)

Which school joined in 1971 and left in 1975?
SELECT school FROM table_name_15 WHERE year_joined = "1971" AND year_left = "1975"
SELECT "school" FROM "table_name_15" WHERE "1971" = "year_joined" AND "1975" = "year_left"