MySQL insert mutiple rows based on SELECT query result

One thing you have to know is that the number of columns returned by your query must match the number of columns you want to insert into

"INSERT INTO NewTable(plan_name, plan_time)    SELECT cp.plan_name, cp.plan_time     FROM courses c         INNER JOIN course_to_plan cpl   ON cpl.course_id = c.course_id         INNER JOIN courseplans cp       ON cp.plan_id = cpl.plan_id    WHERE cpl.course_id = '$course_id'"

Warning: watch out for sql injection through $course_id.

Note that I specified 2 columns in my INSERT statement because the SELECT query return 2 columns

If the number of columns in your table matches the number of columns returned by the query exactly, then you do not need to specify the columns.

Not sure about the php code but if you change your mysql query to an insert/select it should work:

INSERT INTO newtable(plan_name, plan_time)      SELECT cp.plan_name, cp.plan_time       FROM courses c      INNER JOIN course_to_plan cpl               ON cpl.course_id = c.course_id      INNER JOIN courseplans cp                   ON cp.plan_id = cpl.plan_id      WHERE cpl.course_id = '$course_id'