Why does this not Work? I am certain I have oversimplified the mighty T-SQL language. I have some records that get a rollup value based on the records type. Much like an invoice total, except I have to store the rollup for whatever reason. There are about 13 fields to rollup so I have reduced it to one for readability. An overly simplified recordset might look like this;

record #1 IKEY = 101 | MyField = 10 | rTYPE = Item
record #2 IKEY = 102 | MyField = 20 | rTYPE = Item
record #3 IKEY = 103 | MyField = 30 | rTYPE = Item
record #4 IKEY = 100 | MyField = 00 | rTYPE = Rollup
record #5 IKEY = 201 | MyField = 18 | rTYPE = Item
record #6 IKEY = 202 | MyField = 24 | rTYPE = Item

Where the total that should be written to MyField for record IKEY 100 should be 60. I have pulled out all but the meat of the query here:

-- Roll up the values
select 
    sum(MyField) as RollUp
from foo 
    where left(IKey,1) = '1'

 -- insert the rolled up values
 update foo
     set 
        MyField = RollUp
where IKey = '100'

My humble thanks in advance,