Display group title only at the first record within each group

Hi!

Such layout is commonly seen on real world reports where duplicated
group titles are discarded except for the first one.

CREATE TABLE x(name TEXT,dt DATE,amount INTEGER);

COPY x FROM stdin;
john 2016-8-20 80
mary 2016-8-17 20
john 2016-7-8 30
john 2016-8-19 40
mary 2016-8-17 30
john 2016-7-8 50
\.

My desired result follows:

john 2016-07-08 50
30
2016-08-19 40
2016-08-20 80
mary 2016-08-17 20
30

Note that "dt" is sorted as if clause
ORDER BY name,dt
was applied to SELECT.

With this SELECT:

SELECT name
,ROW_NUMBER() OVER (PARTITION BY name) AS rn_name
,dt
,ROW_NUMBER() OVER (PARTITION BY name,dt) AS rn_dt
,amount
FROM x;

I get this result:

john 2 2016-07-08 1 30
john 4 2016-07-08 2 50
john 3 2016-08-19 1 40
john 1 2016-08-20 1 80
mary 1 2016-08-17 1 20
mary 2 2016-08-17 2 30

Above result shows that records are not sorted by rn_name and rn_dt.

Were the above records correctly sorted "BY rn_name,rn_dt", the
following SELECT probably would fulfill my ultimate goal:

SELECT
CASE WHEN rn_name=1 THEN name ELSE NULL END
,CASE WHEN rn_dt=1 THEN dt ELSE NULL END
,amount
FROM (
SELECT name
,ROW_NUMBER() OVER (PARTITION BY name) AS rn_name
,dt
,ROW_NUMBER() OVER (PARTITION BY name,dt) AS rn_dt
,amount
FROM x
) t

Would someone please give me a hand?

Best Regards,
CN

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