fix the fix and update test results for MDEV-4439

mysql-test/suite/innodb/r/innodb_information_schema.result

@@ -51,4 +51,4 @@ RUNNING	4	0	0	7	1	0	REPEATABLE READ	1	1
 trx_isolation_level	trx_unique_checks	trx_foreign_key_checks
 SERIALIZABLE	0	0
 trx_state	trx_isolation_level	trx_last_foreign_key_error
-RUNNING	REPEATABLE READ	`test`.`t2`, CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`c02`) REFERENCES `t1` (`c01`)
+RUNNING	REPEATABLE READ	`test`.`t2`, CONSTRAINT `fk1` FOREIGN KEY (`c02`) REFERENCES `t1` (`c01`)

mysql-test/suite/rpl/r/rpl_mdev382.result

@@ -315,7 +315,7 @@ CREATE TABLE `t``1` ( `a``` INT PRIMARY KEY) ENGINE=innodb;
 CREATE TABLE `t``2` ( `b``` INT PRIMARY KEY, `c``` INT NOT NULL,
 FOREIGN KEY fk (`c```) REFERENCES `t``1`(`a```)) ENGINE=innodb;
 TRUNCATE `t``1`;
-ERROR 42000: Cannot truncate a table referenced in a foreign key constraint (`db1``; select 'oops!'`.`t``2`, CONSTRAINT `t``2_ibfk_1` FOREIGN KEY (`c```) REFERENCES `db1``; select 'oops!'`.`t``1` (`a```))
+ERROR 42000: Cannot truncate a table referenced in a foreign key constraint (`db1``; select 'oops!'`.`t``2`, CONSTRAINT `fk` FOREIGN KEY (`c```) REFERENCES `db1``; select 'oops!'`.`t``1` (`a```))
 DROP TABLE `t``2`;
 DROP TABLE `t``1`;
 *** Test correct quoting of DELETE FROM statement binlogged for HEAP table that is emptied due to server restart

sql/sql_table.cc

@@ -5476,7 +5476,7 @@ handle_if_exists_options(THD *thd, TABLE *table, Alter_info *alter_info)
       if (remove_key)
       {
         push_warning_printf(thd, Sql_condition::WARN_LEVEL_NOTE,
-            ER_DUP_KEYNAME, ER(ER_DUP_KEYNAME), key->name.str);
+            ER_DUP_KEYNAME, ER(ER_DUP_KEYNAME), keyname);
         key_it.remove();
         if (key->type == Key::FOREIGN_KEY)
         {

storage/xtradb/dict/dict0dict.cc

@@ -4242,18 +4242,45 @@ dict_create_foreign_constraints_low(
 		goto loop;
 	}
 
+	if (my_isspace(cs, *ptr)) {
+                ptr1 = dict_accept(cs, ptr, "IF", &success);
+
+                if (success) {
+                        if (!my_isspace(cs, *ptr1)) {
+                                goto loop;
+                        }
+                        ptr1 = dict_accept(cs, ptr1, "NOT", &success);
+                        if (!success) {
+                                goto loop;
+                        }
+                        ptr1 = dict_accept(cs, ptr1, "EXISTS", &success);
+                        if (!success) {
+                                goto loop;
+                        }
+                        ptr = ptr1;
+                }
+	}
+
 	ptr = dict_accept(cs, ptr, "(", &success);
 
 	if (!success) {
-		/* MySQL allows also an index id before the '('; we
-		skip it */
-		ptr = dict_skip_word(cs, ptr, &success);
-
-		if (!success) {
-			dict_foreign_report_syntax_err(
-				name, start_of_latest_foreign, ptr);
+                if (constraint_name) {
+		  /* MySQL allows also an index id before the '('; we
+		  skip it */
+		  ptr = dict_skip_word(cs, ptr, &success);
+		  if (!success) {
+			  dict_foreign_report_syntax_err(
+				  name, start_of_latest_foreign, ptr);
+                          return(DB_CANNOT_ADD_CONSTRAINT);
+                  }
+		}
+                else {
+		  while (my_isspace(cs, *ptr)) {
+			  ptr++;
+		  }
 
-			return(DB_CANNOT_ADD_CONSTRAINT);
+		  ptr = dict_scan_id(cs, ptr, heap,
+				     &constraint_name, FALSE, FALSE);
 		}
 
 		ptr = dict_accept(cs, ptr, "(", &success);
@@ -4727,6 +4754,7 @@ dict_foreign_parse_drop_constraints(
 	char*			str;
 	size_t			len;
 	const char*		ptr;
+        const char*             ptr1;
 	const char*		id;
 	struct charset_info_st*	cs;
 
@@ -4777,6 +4805,16 @@ dict_foreign_parse_drop_constraints(
 		goto syntax_error;
 	}
 
+	ptr1 = dict_accept(cs, ptr, "IF", &success);
+
+	if (success && my_isspace(cs, *ptr1)) {
+	        ptr1 = dict_accept(cs, ptr1, "EXISTS", &success);
+	        if (success) {
+
+                        ptr = ptr1;
+	        }
+	}
+
 	ptr = dict_scan_id(cs, ptr, heap, &id, FALSE, TRUE);
 
 	if (id == NULL) {