update table
 set a1.coulmn=a2.column<
 from table1 as a1, table2 as a2
 where a1.colum1 = a2.column2

;with cte (id, val) as (
 select 1,'A' union all
 select 2,'B' union all
 select 3,'C' 
 )
select *
 into [table1]
 from cte
 
;with cte (id, val) as (
 select 1,'X' union all
 select 2,'Y' union all
 select 3,'Z' 
 )
 select *
 into [table2]
 from cte

select 'Table1',* from [table1]
select 'Table2',* from [table2]

select 'NOW THE UPDATE HAPPENS' as [GASP!!!]

------------------------------------------------------------------
-----------   proper format for using a FROM clause in an update
------------------------------------------------------------------
update table1
 set val=a2.val
 from table1 a1
 join table2 a2 on a1.id = a2.id

-----------   (yes, i used a join instead of tablelist/where)
------------------------------------------------------------------

select 'Table1',* from [table1]

drop table table1
drop table table2

update table1
 set val=a2.val
 from table2 a2
 where table1.id = a2.id

update
  a1
set
  col = a2.col
from
  table1 as a1,
  table2 as a2
where
  a1.col = a2.col

update
  a1
set
  col = a2.col
from
  table1 as a1
  inner join table2 as a2
    on a1.col = a2.col

update table1
 set  somecolumn=a2.column 
 from table2 as a2
 where column1 = a2.column2

update a1
 set  a1.somecolumn=a2.column 
 from table1 as a1, table2 as a2
 where a1.column1 = a2.column2