Implement last_sql()

NAMESPACE

@@ -466,6 +466,7 @@ export(lahman_mysql)
 export(lahman_postgres)
 export(lahman_sqlite)
 export(lahman_srcs)
+export(last_sql)
 export(lazy_base_query)
 export(lazy_frame)
 export(lazy_multi_join_query)

NEWS.md

@@ -1,5 +1,6 @@
 # dbplyr (development version)
 
+* New `last_sql()` retrieves the most recent SQL query generated by dbplyr, which is useful for debugging (#1471).
 * Custom translations of functions starting with `.` work (@MichaelChirico, #1529).
 * SQL Server 2025 (version 17.0) now supports stringr regex functions: `str_detect()`, `str_starts()`, `str_ends()`, `str_replace()`, `str_replace_all()`, `str_remove()`, `str_remove_all()`, `str_extract()`, and `str_count()`. Fixed pattern versions of `str_detect()`, `str_starts()`, and `str_ends()` work on all SQL Server versions (#1671).
 * MS Access now correctly generates SQL for multiple joins by adding required parentheses (#1576).

R/db.R

@@ -49,17 +49,19 @@ db_sql_render <- function(con, sql, ..., cte = FALSE, sql_options = NULL) {
       with = I("db_sql_render(sql_options = sql_options(cte = TRUE))")
     )
     sql_options <- sql_options %||% sql_options(cte = TRUE)
-    out <- db_sql_render(con, sql, ..., sql_options = sql_options)
-    return(out)
   }
 
-  if (is.null(sql_options)) {
-    sql_options <- sql_options()
+  sql_options <- sql_options %||% sql_options()
 
-    out <- db_sql_render(con, sql, ..., sql_options = sql_options)
-    return(out)
-  }
+  out <- db_sql_render_dispatch(con, sql, ..., sql_options = sql_options)
+  the$last_sql <- out
+  return(out)
+
+  # Unusued declaration for roxygen2
+  UseMethod("db_sql_render")
+}
 
+db_sql_render_dispatch <- function(con, sql, ..., sql_options) {
   UseMethod("db_sql_render")
 }
 #' @export

R/remote.R

@@ -106,3 +106,21 @@ remote_query <- function(x, cte = FALSE, sql_options = NULL) {
 remote_query_plan <- function(x, ...) {
   dbplyr_explain(remote_con(x), db_sql_render(remote_con(x), x$lazy_query), ...)
 }
+
+#' Retrieve the last SQL query generated
+#'
+#' This is a helper function that retrieves the most recent SQL query generated
+#' by dbplyr, which can be useful for debugging.
+#'
+#' @return A SQL string, or `NULL` if no query has been generated yet.
+#' @export
+#' @examples
+#' library(dplyr, warn.conflicts = FALSE)
+#'
+#' df <- lazy_frame(x = 1:3)
+#' df |> filter(x > 1)
+#'
+#' last_sql()
+last_sql <- function() {
+  the$last_sql
+}

_pkgdown.yml

@@ -28,6 +28,7 @@ reference:
   - copy_inline
   - pull.tbl_sql
   - show_query
+  - last_sql
   - .sql
 
 - subtitle: Verbs that affect rows

tests/testthat/test-remote.R

@@ -74,3 +74,13 @@ test_that("can retrieve query, src and con metadata", {
   expect_s3_class(remote_query(mf), "sql")
   expect_type(remote_query_plan(mf), "character")
 })
+
+test_that("last_sql() retrieves the most recent query", {
+  lf <- lazy_frame(x = 1:3, y = c("a", "b", "c"))
+
+  lf |> filter(x > 1) |> show_query()
+  expect_match(last_sql(), "WHERE")
+
+  lf |> mutate(z = x + 1) |> show_query()
+  expect_match(last_sql(), "\\+ 1")
+})