title: Oracle: SQL query that returns rows with only numeric values
body: <p>I have a field (column in Oracle) called X that has values like "a1b2c3", "abc", "1ab", "123", "156"</p>
  
  <p>how do I write an sql query that returns me only the X that hold pure numerical values = no letters?  from the example above would be „123“ and „156“</p>
  
  <p>select X
  from myTable
  where ...??</p>