Add median() translation to SQLite

NEWS.md

@@ -1,5 +1,7 @@
 # dbplyr (development version)
 
+* SQLite gets correct translation for `median()` (#357).
+
 * `copy_lahman()` and `copy_nycflights13()` (and hence `nycflights13_sqlite()`)
   and friends now return DBI connections rather than the now deprecated 
   `src_dbi()` (#440).

R/backend-sqlite.R

@@ -35,15 +35,16 @@ sql_translate_env.SQLiteConnection <- function(con) {
       paste0 = sql_paste_infix("", "||", function(x) sql_expr(cast(!!x %as% text))),
       # https://www.sqlite.org/lang_corefunc.html#maxoreunc
       pmin = sql_prefix("MIN"),
-      pmax = sql_prefix("MAX"),
-
+      pmax = sql_prefix("MAX")
     ),
     sql_translator(.parent = base_agg,
-      sd = sql_aggregate("STDEV", "sd")
+      sd = sql_aggregate("STDEV", "sd"),
+      median = sql_prefix("MEDIAN"),
     ),
     if (sqlite_version() >= "3.25") {
       sql_translator(.parent = base_win,
-        sd = win_aggregate("STDEV")
+        sd = win_aggregate("STDEV"),
+        median = win_absent("median")
       )
     } else {
       base_no_win

tests/testthat/test-backend-sqlite.R

@@ -25,6 +25,12 @@ test_that("sqlite mimics two argument log", {
   expect_equal(translate_sql(log(x, 10)), sql('LOG(`x`) / LOG(10.0)'))
 })
 
+test_that("custom aggregates translated", {
+  local_con(simulate_sqlite())
+
+  expect_equal(translate_sql(median(x), window = FALSE), sql('MEDIAN(`x`)'))
+  expect_equal(translate_sql(sd(x, na.rm = TRUE), window = FALSE), sql('STDEV(`x`)'))
+})
 # live database -----------------------------------------------------------
 
 test_that("as.numeric()/as.double() get custom translation", {