生成非重复数字，警惕数据库

I am looking to generate a random number that has no repeats according to a MySQL database. How could I change the following function so that it checks a database if the number(s) generated already exist, and if not, to insert them into a table. Also, how should said table be laid out? I am not the best designing the rows to make them as small (and practical) as possible.I am looking to generate a random number that h