Update MS Access table from nested query

Question

My SQL is very rusty. Am trying to update a counter in a row in a table with a COUNT(*) from that same table in the form of a nested query. The SQL is below:

UPDATE DWInvoiceHeader AS A
SET A.InvCount = (Select Count(B.HIINV) From DWInvoiceHeader AS B 
                  WHERE (B.HIVENT = '0') 
                  Group By B.HIINV 
                  Order By B.HIINV)
WHERE (A.HIVENT = '0');

The rows look like:

HIINV1.......Seq1.....InvCount   - want InvCount to be 3
HIINV1.......Seq2.....InvCount   - want InvCount to be 3
HIINV1.......Seq3.....InvCount   - want InvCount to be 3
HIINV2.......Seq1.....InvCount   - want InvCount to be 2 
HIINV2.......Seq2.....Invcount   - want InvCount to be 2
.
.
.
HIINVn.......Seq1.....InvCount   - want InvCount to be 1

The SQL above gives me the message "Operation must be an updateable query".

Any ideas ?

Answer 1

UPDATE DWInvoiceHeader AS A
SET A.InvCount = 
(
    Select Count(B.HIINV) 
        From DWInvoiceHeader AS B 
        WHERE (B.HIVENT = '0') AND (A.HIINV = B.HIINV)
        Group By B.HIINV 
)
WHERE (A.HIVENT = '0');

Answer 2

You could use the Domain Function Dcount in a way similar to:

UPDATE test
SET InvCount = Dcount("HIVENT","test","[HIVENT]='0'")

If you want to use a generic approach then I would suggest to store the counts in a working table and then update your table joining the working table.

    Select B.HIINV,Count(B.HIINV) as InvCount 
    into WorkingTbl
    From DWInvoiceHeader AS B 
    WHERE (B.HIVENT = '0') AND (A.HIINV = B.HIINV)
    Group By B.HIINV 

   Update   DWInvoiceHeader  A 
   Inner Join WorkingTbl b 
   on a.HIINV=b.HIINV 
   Set A.InvCount=b.InvCount