php - Make ID negative in a JOIN -

I have this query

  SELECT t1 *, T2. * Table 1 to t1 I want to consider "T.Id" (INT type) negative, so basically I just have to add "-" first. "320". I did not try with anything like this:  
  t2.id = 't1.' - 'id'   
 How can I do this? / P>  
 
 
 Use a simple product:  
  t2.id = - 1 * T1.id '