SelectWithUnionQuery (children 2)
 ExpressionList (children 1)
  SelectQuery (children 4)
   ExpressionList (children 1)
    Identifier a
   TablesInSelectQuery (children 1)
    TablesInSelectQueryElement (children 1)
     TableExpression (children 1)
      TableIdentifier t21
   ExpressionList (children 1)
    Identifier a
   Literal UInt64_10
 Identifier Null