Postgresql: Flagging and Identifying Duplicates - postgresql

Question

I'm trying to find a way to mark duplicated cases similar to this question.
However, instead of counting occurrences of duplicated values, I'd like to mark them as 0 and 1, for duplicated and unique cases respectively. This is very similar to SPSS's identify duplicate cases function. For example if I have a dataset like:
Name State Gender
John TX M
Katniss DC F
Noah CA M
Katniss CA F
John SD M
Ariel FL F
And if I wanted to flag those with duplicated name, so the output would be something like this:
Name State Gender Dup
John TX M 1
Katniss DC F 1
Noah CA M 1
Katniss CA F 0
John SD M 0
Ariel FL F 1
A bonus would be a query statement that will handle which case to pick when determining the unique case.

Answer 1

SELECT name, state, gender
, NOT EXISTS (SELECT 1 FROM names nx
WHERE nx.name = na.name
AND nx.gender = na.gender
AND nx.ctid < na.ctid) AS Is_not_a_dup
FROM names na
;
Explanation: [NOT] EXISTS(...) results in a boolean value (which could be converted to an integer) Casting to boolean requires an extra pair of () , though:
SELECT name, state, gender
, (NOT EXISTS (SELECT 1 FROM names nx
WHERE nx.name = na.name
AND nx.gender = na.gender
AND nx.ctid < na.ctid))::integer AS is_not_a_dup
FROM names na
;
Results:
DROP SCHEMA
CREATE SCHEMA
SET
CREATE TABLE
INSERT 0 6
name | state | gender | nodup
---------+-------+--------+-------
John | TX | M | t
Katniss | DC | F | t
Noah | CA | M | t
Katniss | CA | F | f
John | SD | M | f
Ariel | FL | F | t
(6 rows)
name | state | gender | nodup
---------+-------+--------+-------
John | TX | M | 1
Katniss | DC | F | 1
Noah | CA | M | 1
Katniss | CA | F | 0
John | SD | M | 0
Ariel | FL | F | 1
(6 rows)