T-SQL Select join with condition - sql-server

Question

Lets say that i have a 3 tables:
Cars
Id
CarColorHistory
Id
CarID
ColorID
ModificationDate
Color:
Id
ColorName
I want to select all cars and their colors but the important thing is, that color for the car is the last modified color from CarColorHistory table.
I need to use join to do this.
Example:
Cars:
1
2
CarColorhistory:
1 1 1 26/03/2012 -> (actual color, can be take by date or id)
2 1 2 25/03/2012
3 2 2 25/03/2012
Color:
1 Blue
2 Red
I need to get result: (car id, colorName)
1 Blue
2 Red
I tried make it by joining Cars table and CarColorHistory table but I get cars for all colors. I need only actual color (last added).
Please help

Answer 1

Try this:
select c.id, colorname
from cars c
inner join CarColorHistory h on c.id = h.CarID
inner join Color c2 on h.colorid = c2.id
where h.ModificationDate = (select max(ModificationDate)
from CarColorHistory x where c.id = x.CarId)

Answer 2

There are several ways that you can get the result. You can use a subquery to get the max(modificationdate):
select c.id, r.colorname
from cars c
inner join CarColorhistory h1
on c.id = h1.carid
inner join
(
select max(modificationdate) MaxDate,
carid
from CarColorhistory
group by carid
) h2
on h1.carid = h2.carid
and h1.modificationdate = h2.maxdate
inner join color r
on h1.colorid = r.id
See SQL Fiddle with Demo
Or since you are using SQL Server you can use ranking functions:
select id, colorname
from
(
select c.id, r.colorname,
row_number() over(partition by c.id order by modificationdate desc) rn
from cars c
inner join CarColorhistory h1
on c.id = h1.carid
inner join color r
on h1.colorid = r.id
) src
where rn = 1;
See SQL Fiddle with Demo

Answer 3

This should do the trick for you:
SELECT c.id, (
SELECT co.ColorName FROM Color co
WHERE co.id = (
SELECT TOP 1 ColorID FROM CarColorHistory
WHERE CarID = c.id
ORDER BY ModificationDate DESC
)
) AS ColorName

Answer 4

One way to do this might be with just using a subquery, like posted before, since you are using t-sql you should also be able to do it with an apply:
SELECT
Cars.Id, LatestColors.ColorID, LatestColors.ModificationDate
FROM Cars
CROSS APPLY (
SELECT TOP 1
ColorID, ModificationDate
FROM CarColorHistory
WHERE CarID = Cars.ID
ORDER BY ModificationDate DESC
) AS LatestColors

Answer 5

You can try this if you have Sql Server 2005 or greater:
You can try here, how Common table expression is working: Sql Fiddle demo
;WITH CTE_Cars(CarID, MaxDate)
AS
(
SELECT CarID, MAX(ModificataionDate) AS MaxDate
FROM CarColorHistory
GROUP BY CarID
)
SELECT CTE_Cars.CarID, Color.ColorName
FROM
CTE_Cars
INNER JOIN CarColorHistory ON CarColorHistory.CarID = CTE_Cars.CarID AND
CarColorHistory.ModificataionDate = CTE_Cars.MaxDate
INNER JOIN Color ON Color.id = CarColorHistory.ColorId

Answer 6

I'm not sure if this is the best way, but this is the way I do it. First get the values you want out of the tables using the MAX and then use that result as a table to JOIN in order to eliminate unwanted values.
SELECT c.ID, Color.Color
From Cars c JOIN CarColorHistory h on c.id = h.CarID
JOIN Color on h.ColorID = Color.ID
JOIN
--Create a table with only the latest value and the car ID
(
SELECT c.ID, Max(h.TimeStamp) as time
FROM Cars c JOIN CarColorHistory h on c.id = h.CarID
JOIN Color on h.ColorID = Color.ID
Group by c.ID --Join the table on latest time to get rid of old timestamps
) Max on Max.ID = c.ID and h.TimeStamp=max.time