title: postgresql : how to get previous month?
body: <p>In my db, I have <code>date</code> column where the format is like <code>2019-04-01</code> or <code>2019-05-01</code> etc. If it's <code>2019-04-01</code>, I'd like to get <code>2019-03-01</code> , and when it's <code>2019-01-01</code>, I need to have <code>2018-12-01</code> as result.
  I already did some researches however didn't find an exact solution for me.
  Can anyone help me?</p>