avoid defining a one arg hash since it has some invalidation issues

Author: KristofferC

src/join/core.jl

@@ -33,8 +33,7 @@ Base.IndexStyle(::Type{<:OnCol}) = Base.IndexLinear()
     return OnColRow(i, oc.cols, oc.h)
 end
 
-Base.hash(ocr1::OnColRow, h::UInt) = throw(MethodError(hash, (ocr1, h)))
-@inline Base.hash(ocr1::OnColRow) = @inbounds ocr1.h[ocr1.row]
+@inline Base.hash(ocr1::OnColRow, h::UInt) = @inbounds ocr1.h[ocr1.row] ⊻ h
 
 # Hashing one column at a time is faster since it can use SIMD
 function _prehash(oc::OnCol)

test/join.jl

@@ -1000,7 +1000,6 @@ end
     end
 
     for i in eachindex(c1), j in eachindex(oncols, tupcols)
-        @test_throws MethodError hash(oncols[j][1], zero(UInt))
         DataFrames._prehash(oncols[j])
         @test hash(oncols[j][i]) == hash(tupcols[j][i])
         for k in eachindex(c1)