title: select distinct (extract(year from saledate) || extract(month from saledate)) as ym from trnsact order by ym;
body: <p>Working on an exercise question 'How many distinct dates are there in the saledate column of the transaction table for each month/year combination in the database?'  I found a query that works and it is obviously combining the YEAR and MONTH</p>
  
  <pre><code>SELECT DISTINCT (extract(year from saledate) || extract(month from saledate)) as SaleDate
  FROM trnsact
  ORDER BY SaleDate; 
  </code></pre>
  
  <p>But the || is not something we have learned and I cannot find syntax, description or examples anywhere. Can someone please explain?</p>