title: Combine multiple Full Outer Join queries in one query and make ON check on several tables
body: <p>I am quite new to working with SQL (Postgres in my case) and I have a problem when joining several tables in one Query. I am using the <code>FULL OUTER JOIN</code> command for my problem but when table 2 and 3 share same times, they are not combined in a single row but instead create two rows with the same timestamp.</p>
  <p>I have three tables with each a time and a data column:</p>
  <pre><code>time | data1
  12:01  5 
  12:04  7
  12:06  6
  
  time | data2
  12:02  3 
  12:03  4
  12:05  9
  
  time | data3
  12:01  5 
  12:04  7
  12:05  9
  </code></pre>
  <p>And my desired output would be this:</p>
  <pre><code>time | data1 | data2 | data3
  12:01  5       NaN     5
  12:02  NaN     3       NaN
  12:03  NaN     4       NaN
  12:04  7       NaN     7
  12:05  NaN     9       9
  12:06  6       NaN     NaN
  </code></pre>
  <p>This is what I am currently getting, notice how some time stamps are doubled because there is no check if <code>data2.time=data3.time</code>, only <code>data1.time=data2.time</code> and <code>data1.time=data3.time</code></p>
  <pre><code>time | data1 | data2 | data3
  12:01  5       NaN     5
  12:02  NaN     3       NaN
  12:03  NaN     4       NaN
  12:04  7       NaN     7
  12:05  NaN     9       NaN
  12:05  NaN     NaN     9
  12:06  6       NaN     NaN
  </code></pre>
  <p>Notice especially how there is cases where table 1 and 2 share same times where I want to combine the rows and there is cases where table 2 and 3 have the same time in which case i want to combine the rows aswell.
  But I need to do the Join in one single query, so how do I combine these cases in the <code>ON table1.time=table2.time</code> with the <code>table2.time=table3.time</code></p>