title: Select statement Invalid number ORA-01722 Oracle DB
body: <p>Below example works fine, but after try to select statement in <code>IN</code></p>
  
  <p>clause I get the an error.  </p>
  
  <pre><code>select * from emp where empno in ('7839','7698','7782');  --works
  </code></pre>
  
  <p>In my table test column column1 I have --> '7839','7698','7782'</p>
  
  <pre><code>select * from emp where empno in (select column1 from test);
  </code></pre>
  
  <p>The error:</p>
  
  <pre><code>ORA-01722: invalid number
  01722. 00000 -  "invalid number"
  *Cause:    The specified number was invalid.
  *Action:   Specify a valid number.
  </code></pre>
  
  <p>Any solution how fix this, how convert string to number?</p>