Need I lock the table?

[jong-woo choi]

How are you?

I developed an Online-Application System in high school with MySQL and PHP.

I met some troubled situation.

Students select some subject and then applied man become limit.
Then no more application possible.

I wrote the program with PHP.

But I found problem in DataBase.

The column has a number more than limit.


-----------------------------------------------------------------------
mysql> select count(st_num), subject_code from takelecture group by subject_code having count(st_num) > 40;
+---------------+--------------+
| count(st_num) | subject_code |
+---------------+--------------+
| 41 | subj106 |
| 41 | subj18 |
| 41 | subj203 |
| 42 | subj64 |
+---------------+--------------+
4 rows in set (0.01 sec)
--------------------------------------------------------------
Limit number is 40 but some rows have 41,,, have 42,,,

Why this situation caused?

May I use lock? How?

Let me know..please....