sql engine: check if there is more than one element

[randy3k]

When connecting to databases, columns may be of type bit64::integer64. If the length of first_column is less than or equal to 1. diff(first_column) == 1 will throw an error.

Nevertheless, it is not a problem if a database returns integer.

A similar issue has been reported here: https://community.rstudio.com/t/rpostgres-query-works-interactively-in-notebook-but-will-not-knit/14858 But it seems that no one has actually spotted the culprit.

> all(diff(bit64::integer64(1L)) == 1)
Error in if (n2%%n1) warning("length(e2) not a multiple length(e1)") :
  argument is not interpretable as logical

> all(diff(integer(1L)) == 1)
[1] TRUE

[yihui]

Thank you!