CREATE TABLE b (
pk INTEGER AUTO_INCREMENT,
col_varchar_nokey VARCHAR(1),
col_varchar_key VARCHAR(2) GENERATED ALWAYS AS
(CONCAT(col_varchar_nokey, col_varchar_nokey)),
PRIMARY KEY (pk)
);

INSERT INTO b (col_varchar_nokey) VALUES ('v'),('v');

CREATE TABLE d (
pk INTEGER AUTO_INCREMENT,
col_varchar_nokey VARCHAR(1),
col_varchar_key VARCHAR(2) GENERATED ALWAYS AS
(CONCAT(col_varchar_nokey, col_varchar_nokey)),
PRIMARY KEY (pk)
) ;

INSERT INTO d (col_varchar_nokey) VALUES ('q'),('g'),('e'),('l'),(NULL),('v'),('c'),('u'),('x');

CREATE TABLE bb (
pk INTEGER AUTO_INCREMENT,
col_varchar_nokey VARCHAR(1) /*! NULL */,
col_varchar_key VARCHAR(2) GENERATED ALWAYS AS
(CONCAT(col_varchar_nokey, col_varchar_nokey)),
PRIMARY KEY (pk)
);

INSERT INTO bb (col_varchar_nokey) VALUES ('j'),('h');


set optimizer_record_context=ON;

EXPLAIN UPDATE
d AS OUTR1, b AS OUTR2
SET OUTR1.col_varchar_nokey = NULL
WHERE
( 't', 'b' )  IN
(
SELECT
INNR1.col_varchar_nokey AS x,
INNR1.col_varchar_key AS y
FROM bb AS INNR1
WHERE OUTR1.pk = 1
);

SELECT context INTO DUMPFILE 'context1.txt' FROM INFORMATION_SCHEMA.OPTIMIZER_CONTEXT;