Query for finding duplicates - mysql

Question

I am having a table with following schema:
CUSTOMERS (id INT, name VARCHAR(10), height VARCHAR(10), weight INT)
id is the primary key. I want to find out rows in which people who are having exactly same name, same height and same weight. In other words, I want to find out duplicates with-respect-to name, height and weight.
Example table:
1, sam, 160, 100
2, ron, 167, 88
3, john, 150, 90
4, sam, 160, 100
5, rick, 158, 110
6, john, 150, 90
7, sam, 166, 110
Example Output:
Now since there are people with same name, same height and same weight:
sam (id=1), sam (id=4)
and
john (id=3), john (id=6)
I want to get these ids. It is also okay if I get only one id per match (i.e. id=1 from first match and id=3 from second match).
I am trying this query but not sure if it is correct or not.
SELECT id
FROM customers
GROUP BY name, height, weight

Answer 1

Try this (valid for sql server):
SELECT
t.NAME,
'Ids = '+
(
SELECT cast(Id as varchar)+','
FROM Customers c
WHERE c.NAME = t.NAME AND c.Weight = t.Weight AND c.Height = t.Height
FOR XML PATH('')
)
FROM
(
SELECT Name, height, weight
FROM Customers
GROUP BY Name, height, weight
HAVING COUNT(*) > 1
) t
OR
as you asked - only one Id per match
SELECT
t.NAME,
c.Id
FROM
(
SELECT Name, height, weight
FROM Customers
GROUP BY Name, height, weight
HAVING COUNT(*) > 1
) t
JOIN Customers c ON t.NAME AND c.Weight = t.Weight AND c.Height = t.Height

Answer 2

SELECT *
FROM customers C
INNER JOIN
(
SELECT name, height, weight
FROM customers
GROUP BY name, height, weight
HAVING COUNT(*) > 1
) X ON C.name = X.name AND C.height = X.height AND C.weight = X.weight

Answer 3

SELECT c.*
FROM customers c
JOIN (
SELECT name, height, weight
FROM
GROUP BY name, height, weight
HAVING count(*) > 1
) t ON c.name = t.name and c.height = t.height and c.weight = t.weight

Answer 4

you are on the right way:
SELECT min(id)
FROM customers
GROUP BY name, height, weight
HAVING COUNT(*) > 1

Answer 5

I don't know what you are using since you tagged several databases.
In Sql server you won't be able to select the id without putting it in the SELECT.
so if you want to select other fields besides the ones in the group clasue you can use PARTITION BY. Something like this:
SELECT id,
ROW_NUMBER() OVER(PARTITION BY c.name, c.height, c.weight ORDER BY c.name) AS DuplicateCount
FROM customers c
This will give you the ids of the duplicates that you have with the same name, height and weight.
I'm not sure that this is faster that the other solutions though, but, you can profile it and compare.

Answer 6

If it is okay to get only one id per match as you say, you are close to solution:
SELECT
min( id )
,name, height, weight --<-- oncly if you need/want
FROM customers
GROUP BY name, height, weight
HAVING count(*) > 1