From b84be01cd28016569e259a712ec6f8c36087de3a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Kirill=20M=C3=BCller?= <kirill@cynkra.com>
Date: Fri, 6 Oct 2023 17:18:47 +0200
Subject: [PATCH] Work around missing CAST(x AS INTEGER) in MySQL

---
 R/backend-mysql.R                      | 19 +++++++++++++++++--
 tests/testthat/_snaps/backend-mysql.md |  2 +-
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/R/backend-mysql.R b/R/backend-mysql.R
index 85f7bdea8..e1ddab659 100644
--- a/R/backend-mysql.R
+++ b/R/backend-mysql.R
@@ -133,9 +133,24 @@ sql_translation.MariaDBConnection <- function(con) {
 }
 
 #' @export
-sql_translation.MySQL <- sql_translation.MariaDBConnection
+sql_translation.MySQL <- function(con) {
+  maria <- unclass(sql_translation.MariaDBConnection())
+  sql_variant(
+    sql_translator(.parent = maria$scalar,
+      # MySQL doesn't support casting to INTEGER or BIGINT.
+      as.integer = function(x) {
+        sql_expr(TRUNCATE(CAST(!!x %AS% DOUBLE), 0L))
+      },
+      as.integer64 = function(x) {
+        sql_expr(TRUNCATE(CAST(!!x %AS% DOUBLE), 0L))
+      },
+    ),
+    maria$aggregate,
+    maria$window
+  )
+}
 #' @export
-sql_translation.MySQLConnection <- sql_translation.MariaDBConnection
+sql_translation.MySQLConnection <- sql_translation.MySQL
 
 #' @export
 sql_table_analyze.MariaDBConnection <- function(con, table, ...) {
diff --git a/tests/testthat/_snaps/backend-mysql.md b/tests/testthat/_snaps/backend-mysql.md
index c0f110391..a389acf46 100644
--- a/tests/testthat/_snaps/backend-mysql.md
+++ b/tests/testthat/_snaps/backend-mysql.md
@@ -64,7 +64,7 @@
     Code
       copy_inline(con_mysql, tibble(x = 1:2, y = letters[1:2])) %>% remote_query()
     Output
-      <SQL> SELECT CAST(`x` AS INTEGER) AS `x`, CAST(`y` AS CHAR) AS `y`
+      <SQL> SELECT TRUNCATE(CAST(`x` AS DOUBLE), 0) AS `x`, CAST(`y` AS CHAR) AS `y`
       FROM (
         SELECT NULL AS `x`, NULL AS `y`
         WHERE (0 = 1)