title: oracle union caluse: what happens if there is a column name mismatch
body: <p>In oracle, when I do:
  select table1.col1 from table1 union select table2.col2 from table2</p>
  
  <p>It gives me the union of all records and the name of the result column is col1.</p>
  
  <p>Should not this throw an error instead because of mismatch of column names?</p>