Error:can only bind lists of raw vectors (or null)

Question

I have two data frame x and y. I am trying two merge this two data frame using sqldf function in R.

Sqldf::sqldf( select * from x join y on x.key=y.key) But this gives me error

Error:can only bind lists of raw vectors (or null)

I tried separately to run and both of them works Sqldf::sqldf( select * from x) or Sqldf::sqldf( select * from y).