r0 := UnboundTable: t1
  a int64
  b float64

r1 := UnboundTable: t2
  a int64
  b float64

r2 := JoinChain[r0]
  JoinLink[inner, r1]
    r0.a == r1.a
  values:
    a:       r0.a
    b:       r0.b
    b_right: r1.b

CountStar(): CountStar(r2)