title: Impala - Find first day on Month from String value
body: <p>I have data_date column (String data type) in table employee having value in YYYYMMDD format.</p>
  
  <p>Please suggest solution to find first day of month based on data_date column.</p>
  
  <p>for example : </p>
  
  <p>data_Date - 20181217 (String Value)</p>
  
  <p>Output - 20181201 (String Value)</p>