Update Returning into produces error when values don't change

CREATE TABLE t1 (a INT);

INSERT INTO t1 VALUES (1),(2);

UPDATE t1 SET a=a RETURNING a INTO @a;

SELECT @a;

DROP TABLE t1;

At line 7: query 'UPDATE t1 SET a=a RETURNING a INTO @a' failed: ER_SP_FETCH_NO_DATA (1329): No data - zero rows fetched, selected, or processed

CREATE TABLE t1 (a INT);

INSERT INTO t1 VALUES (1);

--error ER_SP_FETCH_NO_DATA

UPDATE t1 SET a=a RETURNING a INTO @a;

SELECT @a;

CREATE TABLE log(i int);

CREATE TRIGGER trg AFTER UPDATE ON t1 FOR EACH ROW INSERT INTO log VALUES (1);

UPDATE t1 SET a=a RETURNING a INTO @a;

SELECT @a;

select * from log;

DROP TABLE t1;

CREATE TABLE t1 (a INT);

INSERT INTO t1 VALUES (1);

UPDATE t1 SET a=a RETURNING a INTO @a;

ERROR 02000: No data - zero rows fetched, selected, or processed

SELECT @a;

@a

NULL

CREATE TABLE log(i int);

CREATE TRIGGER trg AFTER UPDATE ON t1 FOR EACH ROW INSERT INTO log VALUES (1);

UPDATE t1 SET a=a RETURNING a INTO @a;

Warnings:

Warning	1329	No data - zero rows fetched, selected, or processed

SELECT @a;

@a

NULL

select * from log;

i

1

DROP TABLE t1;