SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 3)
   ExpressionList (children 2)
    Identifier data_compressed_bytes
    Identifier data_uncompressed_bytes
   TablesInSelectQuery (children 1)
    TablesInSelectQueryElement (children 1)
     TableExpression (children 1)
      TableIdentifier system.columns
   Function and (children 1)
    ExpressionList (children 3)
     Function equals (children 1)
      ExpressionList (children 2)
       Identifier database
       Function currentDatabase (children 1)
        ExpressionList
     Function equals (children 1)
      ExpressionList (children 2)
       Identifier table
       Literal \'clear_column\'
     Function equals (children 1)
      ExpressionList (children 2)
       Identifier name
       Literal \'num\'
