title: cheapest price for product in month
body: <p>I have a product_prices table</p>
  <pre><code>ID      Product_id     Price   Price_date
  1            1           5      2021-10-01
  2            1           6      2021-10-25
  3            2           5      2021-10-01
  4            2           6      2021-10-25
  5            1           3      2021-09-01
  6            1           5      2021-09-25
  7            2           7      2021-09-01
  8            2           3      2021-09-25
  </code></pre>
  <p>How i can get record what has cheapest price for product in each month by SQL query</p>
  <pre><code>ID      Product_id     Price   Price_date
  1            1           5      2021-10-01
  3            2           5      2021-10-01
  5            1           3      2021-09-01
  8            2           3      2021-09-25
  </code></pre>