Joining multiple tables in Access and limiting to Top 1 result - sql

Question

I have three tables that need to be joined in order to get monthly inventory data in return.
Table 1: TargetInventory
Table 2: TargetValue
Table 3: TargetWeight
[TargetInventory] does not change after being added the first time.
[TargetValue] is just a small table that includes prices of various types of metal.
[TargetWeight] is updated monthly as part of our inventory process. We INSERT new data, we never UPDATE old data.
Below is the relationship between these tables. (Sorry, I don't have the reputation points to post an image. Brand new here, so hopefully this makes sense.)
(* = UniqueKey)
--TargetValue-- --TargetInventory-- --TargetWeight--
*MaterialID <===| *TargetID <=====| *ID
Material |===> MaterialID |===> TargetID
PricePerOunce Length RecordDate
Density Width Weight
Thickness
DateInInventory
The TargetWeight table contains multiple records for TargetID (since a new one is added every month at inventory). That's good for me to track historical usage, but for the current inventory value, I only need the most recent TargetWeight.Weight to be returned.
I don't know how to do a CROSS APPLY from within another INNER JOIN, so I'm at a loss for how to do this (without switching to mySQL and just doing a LIMIT 1...)
I think it needs to look something like what's below, but I'm not sure how to finish the query.
SELECT
TargetInventory.TargetID AS TargetInventory_TargetID,
TargetInventory.MaterialID AS TargetInventory_MaterialID,
TargetInventory.Length,
TargetInventory.Width,
TargetInventory.Thickness,
TargetValue.MaterialID AS TargetValue_MaterialID,
TargetValue.PricePerOunce,
TargetValue.Density,
TargetWeight.ID,
TargetWeight.TargetID AS TargetWeight_TargetID,
TargetWeight.RecordDate,
TargetWeight.Weight
FROM
(TargetValue
INNER JOIN TargetInventory
ON TargetValue.[MaterialID] = TargetInventory.[MaterialID]
)
CROSS APPLY (
SELECT TOP 1 *
FROM .....
)

Answer 1

The following query works for me in Access 2010. It uses an INNER JOIN on a subquery to take the place of the CROSS APPLY (which Access SQL doesn't support). It assumes that there will be no more than one [TargetWeight] record for a given (TargetID, RecordDate):
SELECT
TargetInventory.TargetID AS TargetInventory_TargetID,
TargetInventory.MaterialID AS TargetInventory_MaterialID,
TargetInventory.Length,
TargetInventory.Width,
TargetInventory.Thickness,
TargetValue.MaterialID AS TargetValue_MaterialID,
TargetValue.PricePerOunce,
TargetValue.Density,
LatestWeight.ID,
LatestWeight.TargetID AS TargetWeight_TargetID,
LatestWeight.RecordDate,
LatestWeight.Weight
FROM
(
TargetValue
INNER JOIN
TargetInventory
ON TargetValue.[MaterialID] = TargetInventory.[MaterialID]
)
INNER JOIN
(
SELECT tw.*
FROM
TargetWeight AS tw
INNER JOIN
(
SELECT TargetID, MAX(RecordDate) AS LatestDate
FROM TargetWeight
GROUP BY TargetID
) AS latest
ON latest.TargetID=tw.TargetID
AND latest.LatestDate=tw.RecordDate
) AS LatestWeight
ON LatestWeight.TargetID = TargetInventory.TargetID
Alternative approach specifically for Access 2010 or later
If the above query bogs down with a large number of rows in [TargetWeight] then another possible solution for Access 2010+ would be to add a Yes/No field named [Current] to the [TargetWeight] table and use the following After Insert data macro to ensure that only the latest record for each [TargetID] is flagged as [Current]:
Once that is done, the query would simply be
SELECT
TargetInventory.TargetID AS TargetInventory_TargetID,
TargetInventory.MaterialID AS TargetInventory_MaterialID,
TargetInventory.Length,
TargetInventory.Width,
TargetInventory.Thickness,
TargetValue.MaterialID AS TargetValue_MaterialID,
TargetValue.PricePerOunce,
TargetValue.Density,
TargetWeight.ID,
TargetWeight.TargetID AS TargetWeight_TargetID,
TargetWeight.RecordDate,
TargetWeight.Weight
FROM
(
TargetValue
INNER JOIN
TargetInventory
ON TargetValue.[MaterialID] = TargetInventory.[MaterialID]
)
INNER JOIN
TargetWeight
ON TargetInventory.TargetID = TargetWeight.TargetID
WHERE TargetWeight.Current = True;
To maximize performance, the [TargetWeight].[TargetID] and [TargetWeight].[Current] fields should be indexed.

Answer 2

SELECT TargetInventory.TargetID AS TargetInventory_TargetID,
TargetInventory.MaterialID AS TargetInventory_MaterialID,
TargetInventory.Length,
TargetInventory.Width,
TargetInventory.Thickness,
TargetValue.MaterialID AS TargetValue_MaterialID,
TargetValue.PricePerOunce,
TargetValue.Density, Weight.ID,
Weight.TargetID AS TargetWeight_TargetID,
Weight.RecordDate,
Weight.Weight
FROM TargetInventory
INNER JOIN TargetValue ON TargetValue.[MaterialID] = TargetInventory.[MaterialID]
CROSS APPLY (
SELECT TOP 1 *
FROM TargetWeight
WHERE TargetID = TargetInventory.TargetID
ORDER BY RecordDate DESC
) AS Weight