Explain EXPLAIN QUERY TREE (children 2)
 Set
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 2)
    ExpressionList (children 3)
     Function isNull (children 1)
      ExpressionList (children 1)
       Identifier id
     Function isNull (children 1)
      ExpressionList (children 1)
       Identifier n
     Function isNotNull (children 1)
      ExpressionList (children 1)
       Identifier n
    TablesInSelectQuery (children 1)
     TablesInSelectQueryElement (children 1)
      TableExpression (children 1)
       TableIdentifier t_func_to_subcolumns
