Work around missing CAST(x AS INTEGER) in MySQL

NAMESPACE

@@ -499,6 +499,7 @@ export(simulate_dbi)
 export(simulate_hana)
 export(simulate_hive)
 export(simulate_impala)
+export(simulate_mariadb)
 export(simulate_mssql)
 export(simulate_mysql)
 export(simulate_odbc)

NEWS.md

@@ -1,7 +1,15 @@
 # dbplyr (development version)
 
+## Minor improvements and bug fixes
+
 * `sql_translator()` now checks for duplicated definitions (@krlmlr, #1374).
 
+## Backend specific improvements
+
+* MySQL/MariaDB:
+  * Fix translation of `as.integer()` for MySQL (@krlmlr, #1375).
+  * New `simulate_mariadb()` (@krlmlr, #1375).
+
 # dbplyr 2.4.0
 
 ## Breaking changes

R/backend-mysql.R

@@ -24,7 +24,11 @@ NULL
 
 #' @export
 #' @rdname backend-mysql
-simulate_mysql <- function() simulate_dbi("MariaDBConnection")
+simulate_mysql <- function() simulate_dbi("MySQLConnection")
+
+#' @export
+#' @rdname backend-mysql
+simulate_mariadb <- function() simulate_dbi("MariaDBConnection")
 
 #' @export
 dbplyr_edition.MariaDBConnection <- function(con) {
@@ -129,9 +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, ...) {

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)

tests/testthat/test-backend-mysql.R

@@ -44,7 +44,7 @@ test_that("custom stringr functions translated correctly", {
 # verbs -------------------------------------------------------------------
 
 test_that("generates custom sql", {
-  con_maria <- simulate_mysql()
+  con_maria <- simulate_mariadb()
 
   expect_snapshot(sql_table_analyze(con_maria, in_schema("schema", "tbl")))
   expect_snapshot(sql_query_explain(con_maria, sql("SELECT * FROM table")))
@@ -57,7 +57,7 @@ test_that("generates custom sql", {
 
   expect_snapshot(copy_inline(con_maria, tibble(x = 1:2, y = letters[1:2])) %>% remote_query())
 
-  con_mysql <- simulate_dbi("MySQLConnection")
+  con_mysql <- simulate_mysql()
   expect_snapshot(copy_inline(con_mysql, tibble(x = 1:2, y = letters[1:2])) %>% remote_query())
 })