title: Are left outer joins associative?
body: <p>It's easy to understand why left outer joins are not commutative, but I'm having some trouble understanding whether they are associative. Several online sources suggest that they are not, but I haven't managed to convince myself that this is the case.</p>
  
  <p>Suppose we have three tables: A, B, and C. </p>
  
  <p>Let A contain two columns, ID and B_ID, where ID is the primary key of table A and B_ID is a foreign key corresponding to the primary key of table B.</p>
  
  <p>Let B contain two columns, ID and C_ID, where ID is the primary key of table B and C_ID is a foreign key corresponding to the primary key of table C.</p>
  
  <p>Let C contain two columns, ID and VALUE, where ID is the primary key of table C and VALUE just contains some arbitrary values.</p>
  
  <p>Then shouldn't <code>(A left outer join B) left outer join C</code> be equal to <code>A left outer join (B left outer join C)</code>?</p>