Question: Show names of teachers that teach at least two courses.
Schema: create table teacher (name varchar, teacher_id varchar, PRIMARY KEY (name)); create table course_arrange (teacher_id varchar, PRIMARY KEY (teacher_id))
SQL: select t2.name from course_arrange as t1 join teacher as t2 on t1.teacher_id = t2.teacher_id group by t2.name having count(*) >= 2