CREATE TABLE teachers (firstname VARCHAR2, classroom VARCHAR2)
CREATE TABLE list (classroom VARCHAR2)

Find the first names of the teachers that teach first grade.
SELECT DISTINCT T2.firstname FROM list AS T1 JOIN teachers AS T2 ON T1.classroom = T2.classroom WHERE grade = 1
SELECT DISTINCT "T2"."firstname" FROM "list" "T1" JOIN "teachers" "T2" ON "T1"."classroom" = "T2"."classroom" WHERE "grade" = 1