Question

I need to update col1 in table1 with the highest value in val in table2 that is lower than
col2 in table1. I am trying this:

    update table1 set col1 = max(t2.val)
    from table2 t2 where t2.VAL < col2

I am getting this error:
An aggregate may not appear in the set list of an UPDATE statement.

Here is sample data

Table1
Col1    Col2
2   null
3   null
4   null
6   null
7   null
8   null
9   null
10  null

Table2
Val
1
5

after I run the query I would want it to look like this:

Table1
Col1    Col2
2   1
3   1
4   1
6   5
7   5
8   5
9   5
10  5

Answer 1

UPDATE   t1     SET  
       modified = a.ddd from  t1 t  CROSS APPLY (SELECT MAX(t2.price) AS ddd  from t2 WHERE t2.price<t.val) a

lets initialize t1 (the modified field is the one that will have the max value from t2 but less than its val value)

this is your table1 (t2) with values …

run the query : …

UPDATE   t1     SET  
       modified = a.ddd from  t1 t  CROSS APPLY (SELECT MAX(t2.price) AS ddd  from t2 WHERE t2.price<t.val) a

edit

for your values here is the result :