VB & ASP: Data type mismatch in criteria expression

If you set your field in database as autonumber or integer, you shouldn't state your SQL statement like this:

sql="DELETE from customer WHERE nummer='" & blablabla & "'"

and suppose to be like this

sql="DELETE from customer WHERE nummer=" & blablabla

number is a variable to store a number from form or QueryString for instance... this SQL query need to work...