title: No operator matches the given name and argument type
body: <p>I tried to search in google for what's wrong with my sql statement but with no success! </p>
  
  <blockquote>
    <p>[Err] ERROR:  operator does not exist: character varying * character varying
    LINE 16: "Quantity" * "Unit Price" as "Total"</p>
    
    <p>HINT:  No operator matches the given name and argument type(s). You might need to add explicit type casts.   </p>
  </blockquote>
  
  <pre><code>SELECT
  "Trade Date",
  "Due Date",
  "Reference",
  "Type",
  "Symbol",
  to_number("Quantity", '99999999D99')AS "Quantity",
  to_number("Unit Price", '99999999D99')AS "Unit Price",
  to_number("Amount", '99999999D99')AS "Amount",
  to_number("Commission", '99999999D99')AS "Commission",
  to_number("Charge", '99999999D99')AS "Charge",
  to_number("VAT", '99999999D99')AS "VAT",
  to_number("Net Amount", '99999999D99')AS "Net Amount",
  "W/H",
  to_number("Net Price", '99999999D99')AS "Net Price",
  "Quantity" * "Unit Price" as "Total"
  
  FROM
  "public".aa
  </code></pre>