phpmyadmin dissalow to create more elements in table
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I was thinking if it is possible to forbid to create more elements in table. I have users table and one row only. Can I dissalow to create more rows for anybody from phpmyadmin side. For example to define, that maximum it would be possible to create one line.

Looking for an answer, because somebody just tried to include one more username in my database because of my mistake in php. 