SQL Server - coalesce data on duplicate keys when MERGE-ing - sql-server

Question

I've stumbled across an annoying situation where my source query results have duplicate keys with differing data. Unfortunately I need to back-fill any NULLs.
I tried with a MERGE but I get a key error.
The equivalent query in MySQL (that I cannot convert) is:
Please note that I have changed all the field and table names
INSERT INTO user_brief (name, high_score, colour)
SELECT
u.name,
h.high_score,
p.colour,
FROM foo_table AS f
LEFT JOIN users AS u ON f.user_id = u.id
LEFT JOIN high_scores AS h ON f.user_id = h.id
LEFT JOIN preferences AS p ON f.user_id = p.id
ON DUPLICATE KEY
UPDATE
name = COALESCE(user_brief.name, VALUES(name)),
high_score = COALESCE(user_brief.high_score, VALUES(high_score)),
colour = COALESCE(user_brief.colour, VALUES(colour));
SELECT Query Results
If we take just the SELECT you would get the following results:
name | high_score | color
---------------------------
foo | NULL | brown
foo | 40 | NULL
bar | 29 | blue
...
Desired Results
name | high_score | color
---------------------------
foo | 40 | brown
bar | 29 | blue
...
As you can see it has flattened (not sure if that's the correct term) taking the first non-null value for each column of a name keyed record.
My attempted MERGE solution (but it gets key errors):
MERGE INTO user_brief AS target
USING (SELECT
u.name,
h.high_score,
p.colour,
FROM foo_table AS f
LEFT JOIN users AS u ON f.user_id = u.id
LEFT JOIN high_scores AS h ON f.user_id = h.id
LEFT JOIN preferences AS p ON f.user_id = p.id) AS source
ON target.name = source.name
WHEN MATCHED THEN
UPDATE SET
target.name = COALESCE(source.name, target.name),
target.high_score = COALESCE(source.high_score, target.high_score),
target.colour = COALESCE(source.colour, target.colour)
WHEN NOT MATCHED BY TARGET THEN
INSERT (name, high_score, colour)
VALUES (source.name, source.high_score, source.colour);

Answer 1

You could use GROUP BY to flatten source:
WITH source AS (
SELECT
u.name,
high_score = MIN(h.high_score),
colour = MIN(p.colour)
FROM foo_table AS f
LEFT JOIN users AS u ON f.user_id = u.id
LEFT JOIN high_scores AS h ON f.user_id = h.id
LEFT JOIN preferences AS p ON f.user_id = p.id
GROUP BY u.name
)
MERGE INTO user_brief AS target
USING source
ON target.name = source.name
WHEN MATCHED THEN
UPDATE SET
target.name = COALESCE(source.name, target.name),
target.high_score = COALESCE(source.high_score, target.high_score),
target.colour = COALESCE(source.colour, target.colour)
WHEN NOT MATCHED BY TARGET THEN
INSERT (name, high_score, colour)
VALUES (source.name, source.high_score, source.colour);