backend-postgres.md
In dbplyr: A 'dplyr' Back End for Databases

custom window functions translated correctly

Code
  (expect_error(test_translate_sql(quantile(x, 0.3, na.rm = TRUE), window = TRUE))
  )
Output
  <error/rlang_error>
  Error in `quantile()`:
  ! Translation of `quantile()` in `mutate()` is not supported for PostgreSQL.
  i Use a combination of `summarise()` and `left_join()` instead:
    `df %>% left_join(summarise(<col> = quantile(x, 0.3, na.rm = TRUE)))`.
Code
  (expect_error(test_translate_sql(median(x, na.rm = TRUE), window = TRUE)))
Output
  <error/rlang_error>
  Error in `median()`:
  ! Translation of `median()` in `mutate()` is not supported for PostgreSQL.
  i Use a combination of `summarise()` and `left_join()` instead:
    `df %>% left_join(summarise(<col> = median(x, na.rm = TRUE)))`.

custom SQL translation

Code
  left_join(lf, lf, by = "x", na_matches = "na")
Output
  <SQL>
  SELECT `df_LHS`.`x` AS `x`
  FROM `df` AS `df_LHS`
  LEFT JOIN `df` AS `df_RHS`
    ON (`df_LHS`.`x` IS NOT DISTINCT FROM `df_RHS`.`x`)

Code
  copy_inline(con, tibble(x = integer(), y = character())) %>% remote_query()
Output
  <SQL> SELECT CAST(NULL AS INTEGER) AS `x`, CAST(NULL AS TEXT) AS `y`
  WHERE (0 = 1)

Code
  copy_inline(con, tibble(x = 1:2, y = letters[1:2])) %>% remote_query()
Output
  <SQL> SELECT CAST(`x` AS INTEGER) AS `x`, CAST(`y` AS TEXT) AS `y`
  FROM (  VALUES (1, 'a'), (2, 'b')) AS drvd(`x`, `y`)

`sql_query_insert()` works

Code
  (sql_query_insert(con = con, table = ident("df_x"), from = sql_render(df_y, con,
    lvl = 1), insert_cols = colnames(df_y), by = c("a", "b"), conflict = "error",
  returning_cols = c("a", b2 = "b")))
Condition
  Error in `sql_query_insert()`:
  ! `conflict = "error"` isn't supported on database backends.
  i It must be "ignore" instead.

Code
  sql_query_insert(con = con, table = ident("df_x"), from = sql_render(df_y, con,
    lvl = 1), insert_cols = colnames(df_y), by = c("a", "b"), conflict = "ignore",
  returning_cols = c("a", b2 = "b"))
Output
  <SQL> INSERT INTO `df_x` (`a`, `b`, `c`, `d`)
  SELECT *
  FROM (
    SELECT `a`, `b`, `c` + 1.0 AS `c`, `d`
    FROM `df_y`
  ) AS `...y`
  ON CONFLICT (`a`, `b`)
  DO NOTHING
  RETURNING `df_x`.`a`, `df_x`.`b` AS `b2`

`sql_query_upsert()` with method = 'on_conflict' is correct

Code
  sql_query_upsert(con = con, table = ident("df_x"), from = sql_render(df_y, con,
    lvl = 1), by = c("c", "d"), update_cols = c("a", "b"), returning_cols = c("a",
    b2 = "b"), method = "on_conflict")
Output
  <SQL> INSERT INTO `df_x` (`c`, `d`, `a`, `b`)
  SELECT `c`, `d`, `a`, `b`
  FROM (
    SELECT `a`, `b`, `c` + 1.0 AS `c`, `d`
    FROM `df_y`
  ) AS `...y`
  WHERE true
  ON CONFLICT  (`c`, `d`)
  DO UPDATE
  SET `a` = `excluded`.`a`, `b` = `excluded`.`b`
  RETURNING `df_x`.`a`, `df_x`.`b` AS `b2`

can explain

Code
  db %>% mutate(y = x + 1) %>% explain()
Output
  <SQL>
  SELECT "test".*, "x" + 1.0 AS "y"
  FROM "test"

  <PLAN>
                                             QUERY PLAN
  1 Seq Scan on test  (cost=0.00..1.04 rows=3 width=36)

Code
  db %>% mutate(y = x + 1) %>% explain(format = "json")
Output
  <SQL>
  SELECT "test".*, "x" + 1.0 AS "y"
  FROM "test"

  <PLAN>
                                                                                                                                                                                                                                                                                            QUERY PLAN
  1 [\n  {\n    "Plan": {\n      "Node Type": "Seq Scan",\n      "Parallel Aware": false,\n      "Async Capable": false,\n      "Relation Name": "test",\n      "Alias": "test",\n      "Startup Cost": 0.00,\n      "Total Cost": 1.04,\n      "Plan Rows": 3,\n      "Plan Width": 36\n    }\n  }\n]

can insert with returning

Code
  rows_insert(x, y, by = c("a", "b"), in_place = TRUE, conflict = "ignore",
  returning = everything(), method = "on_conflict")
Condition
  Error in `rows_insert()`:
  ! Can't modify database table "df_x".
  Caused by error:
  ! dummy DBI error

can upsert with returning

Code
  rows_upsert(x, y, by = c("a", "b"), in_place = TRUE, returning = everything(),
  method = "on_conflict")
Condition
  Error in `rows_upsert()`:
  ! Can't modify database table "df_x".
  Caused by error:
  ! dummy DBI error