Fix should_change_user for mysql 5.6

Author: blackbeam

src/conn/mod.rs

@@ -1547,17 +1547,23 @@ mod test {
             &["mysql_native_password"]
         };
 
-        for plugin in plugins {
+        for (i, plugin) in plugins.iter().enumerate() {
             let mut rng = rand::thread_rng();
             let mut pass = [0u8; 10];
             pass.try_fill(&mut rng).unwrap();
             let pass: String = IntoIterator::into_iter(pass)
                 .map(|x| ((x % (123 - 97)) + 97) as char)
                 .collect();
 
-            conn.query_drop("DROP USER /*!50700 IF EXISTS */ /*M!100103 IF EXISTS */ __mats")
-                .await
-                .unwrap();
+            let result = conn
+                .query_drop("DROP USER /*!50700 IF EXISTS */ /*M!100103 IF EXISTS */ __mats")
+                .await;
+            if matches!(conn.server_version(), (5, 6, _)) && i == 0 {
+                // IF EXISTS is not supported on 5.6 so the query will fail on the first iteration
+                drop(result);
+            } else {
+                result.unwrap();
+            }
 
             if conn.inner.is_mariadb || conn.server_version() < (5, 7, 0) {
                 if matches!(conn.server_version(), (5, 6, _)) {