User   UserDate
Петя   2024-01-01
Петя   2024-01-01
Петя   2026-01-01
Ваня   2025-01-02
Ваня   2025-01-02
Игорь  2025-06-10

{
   Петя: {
       '2024-01-01': 2,
	   '2026-01-01': 1
   }.
   Ввня: {
       '2025-01-02': 2
   }
   Игорь: {
	    '2025-06-10': 1
   }
} 

WITH tmp AS(
	SELECT
		COUNT(*) AS "kolvo",
		"UserData"
		"User"

	FROM  "Users"
	GROUP BY "User",  "UserData"
),
tmp1 AS(
	SELECT 
		"User",
		array_agg(
			json_build_object(
				"UserDate"::text, "Kol"
			)
		) AS "user_json"
	GROUP BY "User"
)	

SELECT 
	array_agg(
		json_build_object(
			"User", "user_json"
		)
	)
FROM tmp1