SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 3)
   ExpressionList (children 2)
    Identifier t1.a (alias t1_a)
    Identifier t2.a (alias t2_a)
   TablesInSelectQuery (children 2)
    TablesInSelectQueryElement (children 1)
     TableExpression (children 1)
      TableIdentifier source_table1 (alias t1)
    TablesInSelectQueryElement (children 2)
     TableExpression (children 1)
      TableIdentifier source_table1 (alias t2)
     TableJoin (children 1)
      Function equals (children 1)
       ExpressionList (children 2)
        Identifier t1_a
        Identifier t2_a
   Literal UInt64_1