Explain this for me please.

[zooman]

Remember to prefix the table, if you do not know what is a prefix or
you don't use it then you can run the queries without any changes

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ALTER TABLE attachment add usedin varchar(30) not null;
ALTER TABLE attachment add itemid int not null;
ALTER TABLE pmtext add attach int not null;
ALTER TABLE attachment add index (usedin,itemid);

Can some one explain what a prefix is please?

And what it means by ?Remember to prefix the table? I would be very grateful if someone could show an eg.

Regards,
Zooman