How to query postgresql for duplicate count and deduplication query

SELECT id, name, email,
count(*) over (partition by email) cnt
FROM people

SELECT id, name, email,
row_number() over (PARTITION BY email ORDER BY id DESC) AS row_num
FROM people

select distinct on (a) a,b,c from t_distinct;

select distinct a,b,c from t_distinct;

SELECT Number,property,count(*) over (PARTITION BY Number) AS “row_num”
from (select Number,‘Need to change the terminal user' as attribute from "Market Department 0330 needs to be replaced with terminal user details" union
 SELECT number, ‘Card slot needs to be replaced’ as property FROM “Marketing Department0330Need to upgrade the terminal version to openVoLTEReplace the switch slot”) as ss

SELECT Number,property,row_number() over (PARTITION BY Number ORDER BY Number DESC) AS “row_num”
from (select Number,‘Need to change the terminal user' as attribute from "Market Department 0330 needs to be replaced with terminal user details" union
 SELECT number, ‘Card slot needs to be replaced’ as property FROM “Marketing Department0330Need to upgrade the terminal version to openVoLTEReplace the switch slot”) as ss