how to know this row has been referenced or not????

Assume I have one table:
id    name    comment
1     stupid  blabla
2     idiot   blabla

These row has been referenced by other table..... Then I add one row to
that table, so the table become:
id    name    comment
1     stupid  blabla
2     idiot   blabla
3     dumb    bleble

The row with id "3" has not been referenced by other table because I
have just insert it ( it is still fresh ).... How do I know for sure
that "this row" or "that row" has or has not been referenced by other
table???? Of cource I can test it by trying to delete it.... if it has
been referenced, the delete command will fail, and if it has not been
referenced the delete command will success.....

Thank you.