title: Using inner join to reduce results. Do I need to reference new table anywhere beyond the join statement?
body: <p>I'm wondering if I can just do an inner join as kind of a where clause by itself. Or if I use a field from the joined table in my where clause, if it's redundant.</p>
  
  <pre><code>    select * from T1   inner join T2   on T1.id = T2.id   where T2.z is not null
  </code></pre>
  
  <p>Is the "T2.z is null" part redundant if all I want returned are records in T1 where the same id exists in T2?</p>