no, using multiple is not correct.
you should only have one Primary key column.
the primary key column should use an Integer as the data type, and it should be set to automatically increment.
the primary key column should be a numeric value that is controlled by the database.
The section, school year and semester columns can be indexes in the table, but they will not be the primary key.
the way I would create the table is:
classID - Primary Key, auto increment
classSection - text
classYear - text
classSemester
you will have records that look like this:
+---------+--------------+-------------+---------------+
| classID | classSection | classYear | classSemester |
+---------+--------------+-------------+---------------+
| 1 | M001 | 2001 - 2012 | First |
+---------+--------------+-------------+---------------+
| 2 | M001 | 2001 - 2012 | Second |
+---------+--------------+-------------+---------------+
| 3 | M001 | 2001 - 2012 | Third |
+---------+--------------+-------------+---------------+
| 4 | M001 | 2001 - 2012 | Fourth |
+---------+--------------+-------------+---------------+
the value to use to create the relationship to a first semester or third semester class would be the classID column.
I strongly suggest looking at your local bookstore for some books on MySQL database design.
