SQL 16 Populate total number of employee working in Department

Here we have Simple basic table structure same as  of Emp dept tables available in Oracle .

Here we need to Find the total number of employees working in Department. I am adding various alternate ways of doing this task. 

Table Employee Data Structure

Id	Name	DeptId
1	A	10
2	B	10
3	C	10
4	D	10
5	E	20
6	F	20
7	G	20
8	H	30
9	I	30

Table Department Data Structure

DeptId	Name
10	Sales
20	Dev
30	Tester

Expected Output

Id	Name	DeptId	Count
1	A	10	4
2	B	10	4
3	C	10	4
4	D	10	4
5	E	20	3
6	F	20	3
7	G	20	3
8	H	30	2
9	I	30	2

Create table Query 

SELECT *
INTO SQL16
FROM (
	SELECT 1 id
		, 'A' name
		, 10 deptid
	
	UNION ALL
	
	SELECT 2
		, 'B'
		, 10
	
	UNION ALL
	
	SELECT 3
		, 'C'
		, 10
	
	UNION ALL
	
	SELECT 4
		, 'D'
		, 10
	
	UNION ALL
	
	SELECT 5
		, 'E'
		, 20
	
	UNION ALL
	
	SELECT 6
		, 'F'
		, 20
	
	UNION ALL
	
	SELECT 7
		, 'G'
		, 20
	
	UNION ALL
	
	SELECT 8
		, 'H'
		, 30
	
	UNION ALL
	
	SELECT 9
		, 'I'
		, 30
	) t

Alternate Solution 1

SELECT *
INTO SQL16_1
FROM (
	SELECT 10 id
		, 'Sale' Dname
	
	UNION ALL
	
	SELECT 20
		, 'Dev'
	
	UNION ALL
	
	SELECT 30
		, 'QA'
	) t1

Alternate Solution 2
SELECT ID
	, NAME
	, DEPTID
	, COUNT(*) OVER (
		PARTITION BY DEPTID ORDER BY DEPTID
		) AS CUMMULATIVE_SUM
FROM SQL16;

Alternate Solution 3
SELECT ID
	, NAME
	, DEPTID
	, (
		SELECT SUM(1) CUMMULATIVE_SUM
		FROM SQL16 CI
		WHERE CI.DEPTID = CO.DEPTID
		GROUP BY DEPTID
		) AS CUMMULATIVE_SUM
FROM SQL16 CO;

Alternate Solution 4
SELECT CO.ID
	, CO.NAME
	, CO.DEPTID
	, (
		CASE 
			WHEN CI.DEPTID = CO.DEPTID
				THEN SUM(1) OVER (
						PARTITION BY CO.DEPTID ORDER BY CO.DEPTID
						)
			END
		) AS CUMMULATIVE_SUM
FROM SQL16 CO
JOIN SQL16 CI ON CO.ID = CI.ID;

Alternate Solution 5
SELECT *
FROM SQL16 p14
LEFT JOIN (
	SELECT count(*) cnt
		, deptid
	FROM SQL16
	GROUP BY deptid
	) t1 ON t1.deptid = p14.deptid