feat: add two utility functions export_parquet and create_view and a vignette on how to materialize data.

[nbc]

This PR add two utility functions :

• export_parquet uses COPY TO to export a parquet file from a tbl_lazy
• create_view creates a view based on a tbl_lazy

The vignette explains how to materialize data using these two functions, as well as with the lesser-known dbplyr::compute() function.

Fixes #207, #630

[krlmlr]

Thanks for the effort. The code looks good, I'm still not ready to assume maintenance for it.

I labeled the issues as "help wanted" before duckplyr 1.1.0. Writing to Parquet works there:

library(tidyverse)
library(duckdb)
#> Loading required package: DBI

con <- dbConnect(duckdb::duckdb())

dbWriteTable(con, "my_tbl", data.frame(a = 1))

dbplyr_tbl <- tbl(con, "my_tbl")

dbplyr_tbl %>%
  duckplyr::as_duckdb_tibble() |>
  duckplyr::compute_parquet("my_tbl.parquet")
#> # A duckplyr data frame: 1 variable
#>       a
#>   <dbl>
#> 1     1

duckplyr_parquet <-
  duckplyr::read_parquet_duckdb("my_tbl.parquet")
duckplyr_parquet
#> # A duckplyr data frame: 1 variable
#>       a
#>   <dbl>
#> 1     1

^{Created on 2025-06-17 with reprex v2.1.1}

As for creating a view, dbplyr or a related package is a better fit, this functionality seems general enough to work across databases.

I'd like to keep the package vignette-free for shorter build times. Otherwise, each R CMD build . will have to install the package.

Happy to see this code thrive elsewhere!