SQL Server: how to include count in the select query with where clause? - sql

Question

Let's say I have this table:
id out flag
--- --- ---
1 0 1
1 1 0
1 4 0
2 0 1
2 2 0
2 2 0
3 0 1
3 2 0
3 1 0
3 4 0
I want to count the number of rows with out=(0, 2, or 4) and later display rows where flag = 1
Basically:
select id, count(where out IN(0,2,4)) as cnt where flag = 1
My desired output:
id cnt
--- ----
1 2
2 3
3 3
This query works as expected but only when I don't have "where flag = 1":
select id,sum(case when out in (0,2,4) then 1 else 0 end) over(partition by id) as cnt
from tablename
Is there a way for me to calculate sum() of something first and store it in a column, and later filter out rows using where clause? currently what's happening is that rows are being filtered out first and later sum(...) is calculated.
Any way I can rectify this?

Answer 1

You can use a case expression to sum only rows for an id when they have specified values for the out column.
select id,sum(case when out in (0,2,4) then 1 else 0 end) as cnt
from tablename
group by id
Edit: To include other columns when summing, use the sum window function.
select * from (select id,flag
,sum(case when out in (0,2,4) then 1 else 0 end) over(partition by id) as cnt
--include other columns as required
from tablename
) x
where flag=1

Answer 2

select id,count(*) as cnt
from tablename
where out in (0,2,4)
group by id

Answer 3

Do count for 0,2,4 OUT. And then filter them with a Inner Join or using Correlated subquery
Schema:
CREATE TABLE #TAB (ID INT, OUT_VALUE INT, FLAG INT)
INSERT INTO #TAB
SELECT 1, 0, 1
UNION ALL
SELECT 1, 1, 0
UNION ALL
SELECT 1, 4, 0
UNION ALL
SELECT 2, 0, 1
UNION ALL
SELECT 2, 2, 0
UNION ALL
SELECT 2, 2, 0
UNION ALL
SELECT 3, 0, 1
UNION ALL
SELECT 3, 2, 0
UNION ALL
SELECT 3, 1, 0
UNION ALL
SELECT 3, 4, 0
UNION ALL
SELECT 4, 4, 0
Now do select like below
INNER JOIN
SELECT T1.ID,COUNT(1) C
FROM #TAB T1
INNER JOIN
(
SELECT DISTINCT ID FROM #TAB WHERE FLAG = 1
)FLAGS ON T1.ID = FLAGS.ID
WHERE T1.OUT_VALUE IN (0,2,4)
GROUP BY T1.ID
Correlated Sub-query
SELECT ID, C FROM (
SELECT T1.ID
,COUNT(1) C
,(
SELECT DISTINCT ID
FROM #TAB T2
WHERE T1.ID = T2.ID
AND T2.FLAG = 1
) FLAG
FROM #TAB T1 WHERE T1.OUT_VALUE IN (0,2,4)
GROUP BY T1.ID
)A
WHERE A.FLAG IS NOT NULL
The result will be
+----+---+
| ID | C |
+----+---+
| 1 | 2 |
| 2 | 3 |
| 3 | 3 |
+----+---+