drop table if exists tab1;

drop table if exists tab2;

create table tab1 (c1 int, c2 int);

create table tab2 (c3 int);

insert tab1 values (1,2);

insert tab2 values (0);

-- first we make a multiple-table update:

update tab1, tab2 set c1 = c2, c2 = c1;

select * from tab1;

/* 

output:

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

| c1   | c2   |

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

|    2 |    1 |

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

If evalutation was left-to-right, then the result should be "2" in both columns, but it seems like this statement "evaluates all assignments simultaneously".

*/

-- and now a single-table update:

update tab1       set c1 = c2, c2 = c1;

select * from tab1;

/* output:

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

| c1   | c2   |

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

|    1 |    1 |

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

Here evalutation is "left-to-right".

*/