Sequential left Joins behave as inner Joins
<p>I have the following data in 3 tables:</p>

<pre><code>  materials          customers             sales
 -----------        -----------        --------------   
  mtrl comp         cust  comp        mtrl  cust  expqty
    1   2            22    2           1     22     1
    2   2            23    2           2     22     2
    3   2            24    2           3     23     3
    4   2            25    2           4     24     4
</code></pre>

<p>and I want to produce the following result:</p>

<pre><code>mtrl  cust  expqty  
 1     22     1  
 2     22     2  
 3     22    null  
 4     22    null
</code></pre>

<p>In SQL Server I am using the following query:</p>

<pre><code>select a.mtrl,b.cust,c.expqty from materials a left join customers b on a.comp=b.comp 
left join sales c on c.mtrl=a.mtrl and c.cust=b.cust where b.cust=22
</code></pre>

<p>and although I am using a left join, I loose the last 2 lines and all I get is:</p>

<pre><code>   mtrl  cust  expqty  
     1     22     1  
     2     22     2  
</code></pre>

<p>Can you advice me on what I am doing wrong or how would I achieve the desired result? </p>