如何在一列更新mysql时限制另一列的更新？

i have table called post_data having username,email,pass,cam_name,upd_date(of type datatime) fields in that. but the problem is when i insert username, email pass into the table that upd_date(datatime) is updated with current data and time. how can i restrict that ...

I even change the datatype form DATETIME to TIMESTAMP

No use..still it stores current date and time when i update only certain columns.

can any tell me ...

You have set the default datetime for that column. You need to alter the column.

 alter table post_data alter column upd_date drop default;

If your column doesn't accept NULL, then it will implicitly set default value. You need to alter you table to allow null.

Data Type Default Values

If a column definition includes no explicit DEFAULT value, MySQL determines the default value

ALTER TABLE post_data MODIFY upd_date datetime null;