SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 3)
   ExpressionList (children 1)
    Asterisk
   TablesInSelectQuery (children 2)
    TablesInSelectQueryElement (children 1)
     TableExpression (children 1)
      TableIdentifier t
    TablesInSelectQueryElement (children 2)
     TableExpression (children 1)
      TableIdentifier s
     TableJoin (children 1)
      Function and (children 1)
       ExpressionList (children 2)
        Function equals (children 1)
         ExpressionList (children 2)
          Identifier t.a
          Identifier s.a
        Function equals (children 1)
         ExpressionList (children 2)
          Identifier t.b
          Identifier s.b
   Function isNull (children 1)
    ExpressionList (children 1)
     Identifier s.a