title: Retrieving database associations and filling with NULL value when no association exists
body: <p>I have three Postgresql tables associateds to another table:</p>
  
  <p>USER (id_user, first_name, last_name)</p>
  
  <p>ADDRESS (id_address, id_user, address)</p>
  
  <p>BANK_CARD (id_bank_card, id_user, number)</p>
  
  <p>NETWORK (id_network, id_user, status)</p>
  
  <p>A user can have multiple addresses, bank cards and networks.</p>
  
  <p>For instance for USER table:</p>
  
  <pre><code>id_user    first_name     last_name
  -------------------------------------
   1          John           Doe
   2          David          Smith
  </code></pre>
  
  <p>For ADDRESS table:</p>
  
  <pre><code>id_address    id_user    address
  ----------------------------------
   10            1          address1
  </code></pre>
  
  <p>For BANK_CARD:</p>
  
  <pre><code>id_bank_card    id_user     number
  -----------------------------------
   20              1           1234
   21              1           5678
  </code></pre>
  
  <p>For NETWORK:</p>
  
  <pre><code>id_network    id_user    status
  --------------------------------
   30            1          status1
   31            1          status2
   32            1          status3
  </code></pre>
  
  <p>I want to retrieve the existing associations between a user and the other tables as follows:</p>
  
  <pre><code>id_user  id_address  address  id_bank_card  number  id_network  status
  -----------------------------------------------------------------------
   1        10         address1      20       1234       30       status1
   1        NULL       NULL          21       5678       31       status2
   1        NULL       NULL          NULL     NULL       32       status3
  </code></pre>
  
  <p>I have tried different queries using JOIN or UNION but nothing works. Thank you for helping.</p>