VBA Iteration vs SQL Speed in Access - sql

Question

Goal: I have a bunch of dates, I want to update the records of the minimum date by category:
JVID APDATE TAG into > JVID APDATE TAG
1 201501 Use 1 201501 Don't Use
1 201502 Use 1 201502 Use
1 201502 Use 1 201502 Use
1 201503 Use 1 201503 Use
2 201502 Use 2 201502 Don't Use
2 201503 Use 2 201503 Use
The method I'm using is as follows:
I create a dictionary where the Key = ID, and Value = MinDateByID
Then I loop thorough the keys (for each key in dictionary) and run an update query for each ID that checks an IIF statement updating Use/Don't Use based on the date matching the min date.
This works, but w/ +80k IDs covering +1M records it takes forever.
I'm considering running the same thing, but dumping SQL and just iterating through the records, but I can't imagine that'd be faster?
I'm looking for SQL or VBA suggestions.
Thank you in advance!
EDIT - Added SQL From Comments
UPDATE [FY16 Q12 BE] SET [FY16 Q12 BE].[Record Use] = IIF([FY16 Q12 BE].[Date] = "201601", "Use", "Don't Use") WHERE ([FY16 Q12 BE].[ID]="20165645699");
I look through each of the dictionary key/value pairs ex (20165645699, 201601)
creating and running this script in various forms 80k+ times

Answer 1

MS Access is more restrictive than mainstream databases in joined updates, so I had to use a temporary table T2 to hold the minimum values.
SELECT T1.ID, MIN(T1.RDate) AS MinDate INTO T2
FROM Test1
GROUP BY T1.ID;
Now I can perform the joined update:
UPDATE T1 LEFT JOIN T2
ON T1.ID=T2.ID AND T1.RDate=T2.MinDate;
Finally, I drop the temporary table :
DROP T2;
SET TAG = IIF(T2.ID IS NULL, "Don't Use", "Use");
[I have named your table T1 and the date field RDate to avoid a conflict with a reserved word.]
This could be speeded up further by adding a primary key to T2 on (ID, MinDate) and an index on T1 on (ID, RDate).

Answer 2

I think you can do it with one update query - or at least a combination of multiple queries in one SQL statement.
I'm going to use your example data, since I can't figure out what your actual table or field names are in your comments.
You need to replace Table4 with your table name - and ID/Date/Tag fields to match your column names.
UPDATE SQL:
UPDATE Table4 SET Table4.Tag = "Don't Use"
WHERE ([Date] & "-" & [ID])
In (SELECT MergeID FROM
(SELECT Mins.[MinOfDate] & "-" & [ID] AS MergeID
FROM
(SELECT Table4.ID, Min(Table4.Date) AS MinOfDate
FROM Table4
WHERE Table4.Tag="Use"
GROUP BY Table4.ID) AS Mins) AS Merges);
If you don't need the criteria to only check TAGs that haven't been changed then you can eliminate the criteria WHERE Table4.Tag="Use"
OTHER 'No Tag Check' OPTION
UPDATE SQL:
UPDATE Table4 SET Table4.Tag = "Don't Use"
WHERE ([Date] & "-" & [ID])
In (SELECT MergeID FROM
(SELECT Mins.[MinOfDate] & "-" & [ID] AS MergeID
FROM
(SELECT Table4.ID, Min(Table4.Date) AS MinOfDate
FROM Table4
GROUP BY Table4.ID) AS Mins) AS Merges);

Answer 3

I want to suggest this. But I see you have duplicate dates and I'm not sure how you intend to handle these when you have ties for the earliest date.
update [FY16 Q12 BE]
set TAG = "Don't use"
where not exists (
select 1 from [FY16 Q12 BE] as t2
where t2.ID = [FY16 Q12 BE].ID and t2.[DATE] < [FY16 Q12 BE].[DATE]
)

Answer 4

I settled on an iterative approach - I'm not sure why it's so much faster than the SQL options outline above, but it does the trick. Thank you for your feedback.
Sub MinAPInclude(ByVal Tablename As String)
Dim db As DAO.Database
Dim qd As DAO.QueryDef
Dim rs As DAO.Recordset
Dim strList As String
Dim JVMinAP As Dictionary
Set JVMinAP = New Dictionary
Set db = DBEngine(0)(0)
Dim rst As DAO.Recordset
If Not DoesFieldExist(Tablename, "APDate") Then Exit Sub
SQLStatement = "SELECT [" & Tablename & "].[JVID], Min([" & Tablename & "].[APDate]) AS TargetAP"
SQLStatement = SQLStatement & " FROM [" & Tablename & "]"
SQLStatement = SQLStatement & " GROUP BY [" & Tablename & "].[JVID];"
Set qd = db.CreateQueryDef("", SQLStatement)
Set rs = qd.OpenRecordset
rs.MoveFirst
Do Until rs.EOF
If Not IsNull(rs("JVID")) Then
If Not JVMinAP.Exists(CStr(rs("JVID"))) Then
MinAP = rs("TargetAP")
JVMinAP.Add CStr(rs("JVID")), MinAP
End If
End If
rs.MoveNext
Loop
rs.Close
Set rst = db.OpenRecordset(Tablename)
rst.MoveFirst
Do Until rst.EOF
If rst("Record Use") <> "Include" Then
If rst("APDate") = JVMinAP(CStr(rst("JVID"))) Then
rst.Edit
rst("Record Use") = "Include"
rst.Update
End If
End If
rst.MoveNext
Loop
rst.Close
Set rst = nothing
Set rs = Nothing
Set qd = Nothing
Set db = Nothing
End Sub