Nested ROW comparison executes a ROW-valued stored function twice

CREATE DATABASE row_eval;

USE row_eval;

DELIMITER //

CREATE FUNCTION scalar_fn() RETURNS INT NOT DETERMINISTIC

BEGIN

  SET @calls=COALESCE(@calls,0)+1;

  RETURN 1;

END//

CREATE FUNCTION row_fn() RETURNS ROW(a INT,b INT) NOT DETERMINISTIC

BEGIN

  SET @calls=COALESCE(@calls,0)+1;

  RETURN ROW(1,2);

END//

DELIMITER ;

SET @calls=0;

SELECT ROW(ROW(scalar_fn(),2),3)=ROW(ROW(1,2),3) AS nested_scalar;

SELECT @calls AS scalar_calls;

SET @calls=0;

SELECT row_fn()=ROW(1,2) AS direct_row;

SELECT @calls AS direct_calls;

SET @calls=0;

SELECT ROW(row_fn(),3)=ROW(ROW(1,2),3) AS nested_row;

SELECT @calls AS nested_calls;

SET @calls=0;

SELECT ROW(row_fn(),3)<=>ROW(ROW(1,2),3) AS nullsafe_row;

SELECT @calls AS nullsafe_calls;

PREPARE stmt FROM 'SELECT ROW(row_fn(),3)=ROW(ROW(1,2),3) AS prepared_row';

SET @calls=0;

EXECUTE stmt;

SELECT @calls AS prepared_calls;

DEALLOCATE PREPARE stmt;

DROP DATABASE row_eval;

SET @calls=NULL;

nested_scalar

1

scalar_calls

1

direct_row

1

direct_calls

1

nested_row

1

nested_calls

2

nullsafe_row

1

nullsafe_calls

2

prepared_row

1

prepared_calls

2