title: Left Joins on several tables where any one of them can be master
body: <p>I have simplified my actual live code since I don't want to overflow this post with irrelevant data.</p>
  
  <p>I have (sadly) seven tables, one for each weekday, that contains exactly the same information except for two items and that is the newspaper title and the amount of newspapers the customer should receive. Now any customer can have any number of newspapers (from a single title and all the way up to 20 different titles) and they can have any number of newspapers of that title each day (0 to massive amounts) - BUT! and here comes the kicker - they can have the amount of 0 on any given day.
  What I need in the end is this:</p>
  
  <pre><code>Customer1, New York Times, 0, 7, 3, 2, 2, 10, 10
  </code></pre>
  
  <p>Which would indicate that Customer1 wants 7 New York Tiems on Tuesday (yes, I'm from Sweden, the week DOES start with monday), 10 on saturday and 10 on sunday e.tc.
  Now my 7 different tables I have now will not contain any info at all if the customer doesn't have any papers on that given day which means that I cannot do this:</p>
  
  <pre><code>    select t1.name, t1.title, t1.amount, t2.amount,
             t3.amount, t4.amount, t5.amount, t6.amount,
             t7.amount
      from table_mon t1
      left join table_tue t2 on t2.name = t1.name
      left join table_wen t3 on t3.name = t1.name
      left join table_thu t4 on t4.name = t1.name
      left join table_fri t5 on t5.name = t1.name
      left join table_sat t6 on t6.name = t1.name
      left join table_sun t7 on t7.name = t1.name
  </code></pre>
  
  <p>since monday might be the day that this particular customer dosn't have any paper and thus is not part of the monday table at all. Theoretically he can be in only one of the tables and I have no idea which one.</p>
  
  <p>How can I write a join where I don't know which is the "master" table??</p>