使用Count使用qry中的值并更新到Access 2007中的表

Question

I have a query which counts the number of records for each subset:

SELECT tbl_Interpolation.Unit, tbl_Interpolation.Car, tbl_Interpolation.Pad, 
Nz(Count(tbl_Interpolation.CalenderDate),0) AS NumRecords
FROM tbl_Interpolation
GROUP BY tbl_Interpolation.Unit, tbl_Interpolation.Car, tbl_Interpolation.Pad;

I also have a field in tbl_CalcReg called NumRecords which have the same unit, car and pad as the query above, so where these variables are the same eg tbl_CalcReg.Pad=qry_NumRecords.pad i would like to update the field NumRecords.

Again i am having an issue with the aggregate function, i have looked at DCount() but i cannot seem to find a way to implement it without using criteria, as i just want to count how many calenderdates there are for each Unit/Car/Pad combination. I got as far as DCOUNT("CalenderDate", "tbl_Interpolation", "*") but i really havent a clue as to how i can make this into an update query?

Please help.

Best Regards Donna

Answer 1

You can indeed use DCount() with a query like this

UPDATE tbl_CalcReg SET NumRecords = 
DCount("CalenderDate", "tbl_Interpolation", "Unit=" & Unit & " AND Car=" & Car & " AND Pad=" & Pad)

assuming that [Unit], [Car], and [Pad] are numeric fields. If they are text fields then you'll need to put quotes ( ' ) around the values and escape any quotes in the values themselves.

Answer 2

If I understand correctly, you can do this with a correlated subquery. The following does the update for all records:

update tbl_CalcReg
    set NumRecords = (select count(*)
                      from tbl_Interpolation as i
                      where i.unit = tbl_CalcReg.unit and i.car = tbl_CalcReg.car and
                            i.pad = tbl_CalcReg.pad
                     )

You can add this where clause if you only want changed records:

where NumRecords <> (select count(*)
                     from tbl_Interpolation as i
                     where i.unit = tbl_CalcReg.unit and i.car = tbl_CalcReg.car and
                           i.pad = tbl_CalcReg.pad
                    )

EDIT:

MS Access supports UPDATE / JOIN . In that case:

update tbl_CalcReg JOIN
       (select unit, car, pad, count(*) as cnt
        from tbl_Interpolation
        group by unit, car, pad
       ) as i
       on i.unit = tbl_CalcReg.unit and i.car = tbl_CalcReg.car and i.pad = tbl_CalcReg.pad
    set NumRecords = i.cnt