I run this script:

SET @a=10;

SET @a=20,@b=@a;

SELECT @a,@b;

+------+------+

| @a   | @b   |

+------+------+

|   20 |   10 |

+------+------+

No I wrap the same script into an anonymous SP block:

DELIMITER $$

BEGIN NOT ATOMIC

SET @a=10;

SET @a=20,@b=@a;

SELECT @a,@b;

END

$$

+------+------+

| @a   | @b   |

+------+------+

|   20 |   20 |

+------+------+

Notice:

• in the standalone script @b was assigned to the initial value of @a
• in the anonymous block @b was assigned to the new value of @a

We'll make multiple SET inside an SP work the same way with a standalone SET.

Note, multiple SET for SP variables should also work the same way.