title: How to delete rows in MYSQL where a column doesn't contain certain data
body: <p>A database I am in charge of fixing got filled with spam. There is a table called <strong>url</strong> in the database.  There is a column called <strong>alias</strong>.  There is <strong>2,000 correct alias rows</strong> that should be there and the other <strong>100,000+ are spam</strong>.  I have a comma separated list of all the correct values that should be there.  An example value in Alias would be z6j6h and they are all 5 letters/numbers.  How can I delete every row that does not contain a value in the good list?</p>