title: mysql indexing - joining two tables
body: <p>I have  a table T1 in which 2 columns are c1 and c2 .They are foreign key reference cols to col c3 in tabel U1.
   A query has something like <code>"select ....... from T1, U1 as Ux and U1 as Uy where T1.c1 = 'xyz' and T1.c1 = Ux.c3 and T1.c2 = Uy.c3"</code></p>
  
  <p>Which col , if indexed , give the best results. 
  <code>c1</code> <strong><em>alone</em></strong> or a combination of <code>c1</code> <strong><em>and</em></strong> <code>c2</code> ??</p>