title: Select query causing exception
body: <p>When does the below sql function can cause an exception other than NO DATA FOUND?
  v_ExchangeRate is of type float.The datatype of rate column is NUMBER(14, 10) and this column can not contain NULL values.</p>
  
  <pre><code>BEGIN
  SELECT rate
  INTO v_ExchangeRate
  FROM exchange_rate
  WHERE currency_code = CurrencyCode
  AND status        = 'A';
  </code></pre>
  
  <p>The data type of exchange_rate in database is NUMBER(14,10)</p>
  
  <p><strong>Edit</strong>
  Multiple rows cannot be returned by the where clause as the currency_code is the primary key.</p>