MySQL: Set the character_set_results/character_set_client/character_set_connection session variables on connection setup (#334)

* Support custom mysql_character_set_results configuration in mysql connection pool

* MySQL: Set character set to utf8 on connection setup

* Remove error

---------

Co-authored-by: Phillip LeBlanc <[email protected]>

Author: Sevenannn

src/sql/db_connection_pool/mysqlpool.rs

@@ -57,6 +57,13 @@ pub struct MySQLConnectionPool {
     join_push_down: JoinPushDown,
 }
 
+const SETUP_QUERIES: [&str; 4] = [
+    "SET time_zone = '+00:00'",
+    "SET character_set_results = 'utf8mb4'",
+    "SET character_set_client = 'utf8mb4'",
+    "SET character_set_connection = 'utf8mb4'",
+];
+
 impl MySQLConnectionPool {
     /// Creates a new instance of `MySQLConnectionPool`.
     ///
@@ -160,6 +167,8 @@ impl MySQLConnectionPool {
 
         connection_string = connection_string.ssl_opts(ssl_opts);
 
+        connection_string = connection_string.setup(SETUP_QUERIES.to_vec());
+
         let opts = mysql_async::Opts::from(connection_string);
 
         verify_mysql_opts(&opts).await?;
@@ -209,13 +218,7 @@ impl MySQLConnectionPool {
     /// Returns an error if there is a problem creating the connection pool.
     pub async fn connect_direct(&self) -> super::Result<MySQLConnection> {
         let pool = Arc::clone(&self.pool);
-        let mut conn = pool.get_conn().await.context(MySQLConnectionSnafu)?;
-
-        // Set MySQL session default time zone to UTC to match Datafusion
-        let _: Vec<Row> = conn
-            .exec("SET time_zone = '+00:00'", Params::Empty)
-            .await
-            .context(MySQLConnectionSnafu)?;
+        let conn = pool.get_conn().await.context(MySQLConnectionSnafu)?;
 
         Ok(MySQLConnection::new(conn))
     }
@@ -279,13 +282,7 @@ impl DbConnectionPool<mysql_async::Conn, &'static (dyn ToValue + Sync)> for MySQ
     ) -> super::Result<Box<dyn DbConnection<mysql_async::Conn, &'static (dyn ToValue + Sync)>>>
     {
         let pool = Arc::clone(&self.pool);
-        let mut conn = pool.get_conn().await.context(MySQLConnectionSnafu)?;
-
-        // Set MySQL session default time zone to UTC to match Datafusion
-        let _: Vec<Row> = conn
-            .exec("SET time_zone = '+00:00'", Params::Empty)
-            .await
-            .context(MySQLConnectionSnafu)?;
+        let conn = pool.get_conn().await.context(MySQLConnectionSnafu)?;
 
         Ok(Box::new(MySQLConnection::new(conn)))
     }