Update data where ID match and use case to choose what data - sql

Question

I have two tables
T1:
ID, Truck, Trailer
1 null null
2 null null
T2:
ID, Type, ResourceID
1 R 111
1 F 222
1 D 333
2 R 444
2 F 555
I need a result where
ID, Truck, Trailer
1 111 222
2 444 555
How can I update T1.Truck = T2.ResourceID when T2.Type = R and T1.Trailer = T2.ResourceID when T2.Type = F where T1.ID = T2.ID.
This is what I have so far
UPDATE T1
SET T1.Truck = CASE
WHEN T2.Type = 'R' THEN T2.ResourceId
ELSE T1.Truck
END,
T1.Trailer = CASE
WHEN T2.Type = 'F' THEN T2.ResourceId
ELSE T1.Trailer
END
FROM T1 INNER JOIN (SELECT Id, Type, ResourceId
FROM T2) T2
ON T1.Id = T2.Id
This will only Truck, but not trailer.
What am I missing?

Answer 1

The problem with your current update query is that the update will update one column to null as it can't match both conditions at the same time.
If you did a select * instead of the update the result would look like:
ID Truck Trailer Id Type ResourceId
1 NULL NULL 1 R 111 -- this will set R = 111 and F = null
1 NULL NULL 1 F 222 -- this will set F = 222 and R = null
1 NULL NULL 1 D 333 -- this will set R = null and F = null
2 NULL NULL 2 R 444 -- this will set R = 444 and F = null
2 NULL NULL 2 F 555 -- this will set R = null and F = 555
Here you can see that when Type matches R the update for F will update to null et cetera.
One solution is to join the T2 table twice:
UPDATE T1
SET
T1.Truck = T2.ResourceId
,
T1.Trailer = T3.ResourceId
FROM T1
INNER JOIN (SELECT Id, ResourceId FROM T2 WHERE Type = 'R') T2 ON T1.Id = T2.Id
INNER JOIN (SELECT Id, ResourceId FROM T2 WHERE Type = 'F') T3 ON T1.Id = T3.Id
If there might not always be both types (R,F) then use left join instead of inner join and check for null values.
Edit: thinking a bit more gives this query:
UPDATE T1
SET
T1.Truck = ISNULL(T.rValue, T1.Truck),
T1.Trailer = ISNULL(T.fValue, T1.Trailer)
FROM T1
INNER JOIN (
SELECT
Id,
rValue = MAX(CASE WHEN Type = 'R' THEN ResourceId END),
fValue = MAX(CASE WHEN Type = 'F' THEN ResourceId END)
FROM T2 GROUP BY id
) T ON T1.Id = T.Id
On a side note: using an alias for a derived table that is also a table name can be pretty confusing and should be avoided.

Answer 2

you can PIVOT the table t2 before updating the t1 table
Use the following query to pivot the t2 table.
SELECT ID, R, F
FROM t2
PIVOT (Max(resourceID)
FOR type IN ([R],[F]))pv
Now the result will in the format of t1 table you can easily update using the following query
UPDATE A
SET Trailer = F,
Truck = R
FROM t1 A
INNER JOIN (SELECT ID, R, F
FROM t2
PIVOT (Max(resourceID)
FOR type IN ([R],
[F]))pv) B
ON A.ID = b.ID
SQLFIDDLE DEMO

Answer 3

You can use a JOIN with a condition for each case, so you would JOIN to T2 twice. First on the Id and [Type] = 'R' and again, with [Type] = 'F'.
Here's some runnable sample code:
CREATE TABLE #t1 (id INT, Truck INT, Trailer int)
CREATE TABLE #t2 (id INT, [Type] VARCHAR(1), ResourceId int)
INSERT INTO #t1
( id, Truck, Trailer )
VALUES (1, NULL, NULL),
(2, NULL, NULL)
INSERT INTO #t2
( id, [Type], ResourceId )
VALUES ( 1, 'R', 111),
( 1, 'F', 222),
( 1, 'D', 333),
( 2, 'R', 444),
( 2, 'F', 555)
UPDATE #t1
SET Truck = TR.ResourceId, Trailer = TF.ResourceId
FROM #t1
INNER JOIN #t2 AS TR ON TR.id = #t1.id AND TR.[Type] = 'R'
INNER JOIN #t2 AS TF ON TF.id = #t1.id AND TF.[Type] = 'F'
SELECT * FROM #t1
DROP TABLE #t1
DROP TABLE #t2