Custom errors in mysql trigger [duplicate]

Question

Possible Duplicate:
raise error within MySql function

In MsSQL I can raise a custom error:

CREATE TRIGGER [dbo].[TR__TABLE__DisableRowOnDelete]
ON [dbo].[TABLE]
INSTEAD OF DELETE
AS 
BEGIN
    RAISERROR ('Data cannot be deleted.', 16, 1);
END

How might I do that in MySQL?