SQL SELECT WHERE Trouble any ideas helpful

Question

I have two tables parent and child (related as such on PK/FK GUID)

Child has a Timestamp (the record creation date/time).

What I want to do is get only the most recent child record AND the parent record, FOR EACH parent record.

SELECT 
    dbo_Parents.ParentName, 
    dbo_ChildEntry.CountPropertys, 
    dbo_ChildEntry.DateTimeStamp
FROM 
    dbo_Parents INNER JOIN dbo_ChildEntry 
ON
    dbo_Parents.ParentID = dbo_ChildEntry.ParentID
WHERE 
    ([WHAT SHOULD BE HERE?]))

Answer 1

Assuming that you want the most recent entry, you have to use TOP 1 and order by.

SELECT TOP 1
dbo_Parents.ParentName, 
dbo_ChildEntry.CountPropertys, 
dbo_ChildEntry.DateTimeStamp 
FROM dbo_Parents 
INNER JOIN dbo_ChildEntry ON dbo_Parents.ParentID = dbo_ChildEntry.ParentID 
ORDER BY dbo_ChildEntry.DateTimeStamp desc

Edit after clarification: "the most recent child record AND the parent record, FOR EACH parent record":

WHERE dbo_ChildEntry.DateTimeStamp = 
      ( Select Max( dbo_ChildEntry.DateTimeStamp )
               from dbo_ChildEntry 
               where dbo_Parents.ParentID = dbo_ChildEntry.ParentId )

Answer 2

WHERE dbo.ChildEntry.DateTimeStamp = ( Select Max( c.DateTimeStamp )
                                         from dbo.ChildEntry c
                                        where dbo_Parents.ParentID = c.ParentId )

Answer 3

select p.ParentName, 
    c.CountPropertys, 
    c.DateTimeStamp
from (
    select max(DateTimeStamp) as DateTimeStamp, ParentID
    from dbo_ChildEntry
    group by ParentID) cm
inner join dbo_ChildEntry c on cm.DateTimeStamp = c.DateTimeStamp and cm.ParentID = c.ParentID
inner join dbo_Parents p on c.ParentID = p.ParentID

Answer 4

Since you clarified you'd like one row per parent, try this. For every row, it searches for a child row that has a later timestamp. In the WHERE clause, it filters on rows that do not have a "next" child.

SELECT 
    dbo_Parents.ParentName, 
    cur.CountPropertys, 
    cur.DateTimeStamp
FROM dbo_Parents 
INNER JOIN dbo_ChildEntry cur
    ON dbo_Parents.ParentID = cur.ParentID
LEFT JOIN dbo_ChildEntry next
    ON dbo_Parents.ParentID = next.ParentID
    AND next.DateTimeStamp > cur.DateTimeStamp
WHERE
    next.DateTimeStamp is null

Answer 5

Try

SELECT     dbo_Parents.ParentName,     dbo_ChildEntry.CountPropertys,     
max(dbo_ChildEntry.DateTimeStamp)
FROM     dbo_Parents 
INNER JOIN dbo_ChildEntry ON    dbo_Parents.ParentID = dbo_ChildEntry.ParentID
group by dbo_Parents.ParentName,     dbo_ChildEntry.CountPropertys