Aggregating Child Records at the Parent Level in Access 2010 - sql

Question

The link above will provide an excel sheet with some sample data from both the parent and child table with expected result from the query.
Alright this should be simple but I just can't wrap my head around this for some reason. Pretty much, I have a parent table that is linked to a child table. I want to pull up few of the fields from the child table and merge it with the parent fields. I want to create a view of sort in Access.
The parent record can have multiple child records (1 - many relationship). I want to only pull up one record from the child and merge with the parent. The parent table is called Tank and the child table is Tank_Inspections. The IF statement you see below is a conditional statement that helps in determining which Out of Compliance date I should be pulling up. The issue I'm having is that the Out of Compliance date is tied to inspection type. A Tank can have multiple different inspection types. They query below merges the inspection out of compliance date with few of the tank (parent) fields. However, I want to be able to add more of the child fields (in addition to the inspection out of compliance date) but I can't do that without adding those fields to the group by clause as well. If I do that, then I won't get the right amount of records.
As you can see, the left join is getting all of the records from the parent table which is what I need. If I add any more child table fields to the query, I'll also need to add them to the group by clause and then I'll get more records than what's in the parent table. Essentially, I need to only get the records from the parent table, and then merge child fields in. I may be missing few sub queries... Any suggestions? This is what I have so far and I'm getting the right amount of records. But adding more child fields to the select statement will add more rows than i need...
SELECT parent.tankid, IIf(Min(Nz(child.[tank inspection out of compliance date], #1/1/1901#)) <> #1/1/1901#, Min(child.[tank inspection out of compliance date]), IIf(Min(Nz(child.[tank inspection out of compliance date],#1/1/1901#)) = #1/1/1901# And Max(child.[tank inspection out of compliance date])>Date(), NULL, Min(child.[tank inspection out of compliance date]))) AS [Tank Inspection Out of Compliance Date]
FROM
tank as parent
LEFT JOIN
(
SELECT * FROM tank_inspections WHERE tank_inspections.[actual inspection date] is null
) AS child ON parent.tankid = child.tankid GROUP BY parent.tankid
I was able to modify Parfait suggested query below to come up with this:
SELECT
Site.[Manager] AS PM, Site.[DLA Site Code], Tank.[Name] AS [Name], Tank.[Local Name],
Tank.RPID, Tank.[Fac Num], Tank.[Status], Tank.[Type], Tank.[Capacity], Tank.[Current Prod], IIf(main.[Inspection Out of Compliance Date]<Date() AND NOT IsNull(main.[Inspection Out of Compliance Date]), 'Out of Compliance',
IIf(isnull(main.[Inspection Out of Compliance Date]) OR main.[Inspection Out of Compliance Date]=#1/1/1901#,'Unknown Compliance Status')) AS [Compliance Status], Tank.[EA], Site.Serv, Site.[Name], Tank.Comments, main.[Type], main.[Inspection Out of Compliance Date], main.[Planned Prog Date], main.[Prog Date], main.[Prog Year], main.[Planned Inspection Date], IIf(main.[Inspection Out of Compliance Date]<DateAdd('m',12,Date()) And main.[Prog Date] Is Null,'Action Required') AS [Inspection Planning Action Required], main.[Inspection Comments], tank.TankID, main.inspectionid
FROM
Site INNER JOIN
(
(
(
SELECT ti.tankid, ti.inspectionid, ti.[Type], ti.[Inspection Out of Compliance Date], ti.[Planned Prog Date], ti.[Prog Date], ti.[Prog Year], ti.[Planned Inspection Date], ti.[Inspection Comments] FROM Tank_Inspections AS ti) AS main INNER JOIN Tank ON main.TankID = Tank.TankID) INNER JOIN
(
SELECT [TankID], dlookup("InspectionID", "Tank_Inspections", "[Tank Inspection Out of Compliance Date] " & IIf(Min(Nz([inspection out of compliance date], #1/1/1901#)) <> #1/1/1901#, "= #" & Min([inspection out of compliance date]) & "#", IIf(Min(Nz([inspection out of compliance date],#1/1/1901#)) = #1/1/1901# And Max([inspection out of compliance date])>Date(), "IS NULL", IIF(Min(Nz([inspection out of compliance date],#1/1/1901#)) = #1/1/1901# And Max([inspection out of compliance date])<Date(), "= #" & Min([inspection out of compliance date]) & "#", "IS NULL"))) & " AND TankID = " & TankID & " AND [Actual Inspection Date] is null") AS MinInspectionID FROM Tank_Inspections WHERE [Actual Inspection Date] is null GROUP BY [TankID]
)AS DT ON
(
main.InspectionID = Cint(DT.MinInspectionID)
) AND (main.TankID = DT.TankID)
) ON Site.SiteID = Tank.SiteID
WHERE IIf(main.[Inspection Out of Compliance Date]<Date() And NOT IsNull(main.[Inspection Out of Compliance Date]),'Out of Compliance',IIf(isnull(main.[Inspection Out of Compliance Date]) OR main.[Inspection Out of Compliance Date]=#1/1/1901#,'Unknown Compliance Status'));
I'm close with this query, however, I'm missing a few records. The parent records don't have some of the child records. For example, some of the tank records don't have any inspection records so it's not being pulled. I need to do a left join but can't seem to figure it out with this query. Everything I try doesn't seem to work. Suggestion?

Answer 1

Consider the following query that uses a derived table and joins the unit level parent (Tank) to aggregated child (TankInspections). You can save the derived table as a separate stored query and just replace entire select statement and alias (DT) with query name. I include more aggregates than needed for you to check calculated columns:
SELECT Tanks.*, main.*, DT.MaxInspectionID, DT.MaxInspectionOrComplianceDate
FROM
(TankInspections main
INNER JOIN Tanks ON Tanks.TankID = main.TankID)
INNER JOIN
(
SELECT [TankID],
Max(InspectionID) As MaxInspectionID,
Min([Planned Inspection Date]) As MinInspection,
Max([Planned Inspection Date]) As MaxInspection,
Min([Inspection Out of Compliance Date]) As MinCompliance,
Max([Inspection Out of Compliance Date]) As MaxCompliance,
Max(IIF(([Planned Inspection Date]) Is Null,
IIF(ISNULL([Inspection Out of Compliance Date]),
NULL,
[Inspection Out of Compliance Date]),
[Planned Inspection Date])) As MaxInspectionOrComplianceDate
FROM TankInspections
GROUP BY [TankID]
) As DT
ON main.TankID = DT.TankID
AND main.InspectionID = DT.MaxInspectionID;