title: Date format in sas concatenate with a proc sql under conditions
body: <p>i have a macro_variable :%let date=201909
  and table :</p>
  
  <pre><code>ID   Sending-date  item      
   1   15-jul-2019    A   
   2   23-sep-2019    B  
   3   12-sep-2019    A        
   4    1-jan-2019    B  
   5   5-feb-2019     B       
  </code></pre>
  
  <p>What i'm wondering to do is to verify  if there is an item sent in the month indicated in my date (09 september) and the two previous months (august and july) using a proc sql and without adding new variables.<br>
  the result_table expected is like this :                </p>
  
  <pre><code>Month   Year  Number of items
  9       2019        2
  8       2019        0 
  7       2019        1
  </code></pre>
  
  <p>The biggest problem is how to convert the format of the date in the table like my macro_variable date.        </p>