CREATE TABLE list (lastname CLOB, firstname CLOB, grade NUMBER, classroom NUMBER)
CREATE TABLE teachers (lastname CLOB, firstname CLOB, classroom NUMBER)

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