JOIN vs. LEFT JOIN

Hi !

 

I heard that it is always better to use a full JOIN rather than a LEFT JOIN, for performance reasons.  Is that correct ?

But it's barely possible to use full JOINS all the time, since most of the lookup fields are not required.

Example : in the customer table, the customer type is a looup field to a customer_type table.  But that is not required to post the record.  So I was thinking to create a record in the customer_type table with ID = -1.  And in case the customer type is NULL, to assign it the value -1.  That way, it will be always possible to do a full JOIN.  I was wondering if that is good practice or rather nonsense ?

 

Many thanks in advance,

Nico