Allow overwrite parameter in compute

[carlganz]

library(dplyr)
library(dbplyr)

con <- DBI::dbConnect(RSQLite::SQLite(), ":memory:")
copy_to(con, mtcars)

tbl(con, "mtcars") %>%
  filter(cyl == 4) %>%
# works fine
  compute(temporary = FALSE, name = "mtcars_test")

tbl(con, "mtcars") %>%
  filter(cyl == 4 | cyl == 6) %>%
# error mtcars_test already exists
  compute(temporary = FALSE, name = "mtcars_test", overwrite = TRUE)

I can make a PR if you'd like

[carlganz]

So it turns out this is maybe more complicated than I anticipated. I figure either this function gets an extra overwrite parameter and add if table exists drop table at top if overwrite=TRUE

Or update function here and add dbRemoveTable if it exists and overwrite=T, and put the whole thing inside a transaction.

I don't have a sense of what would be better

[carlganz]

Thanks @mgirlich !!!!