Sum all Inserted Values in Trigger - sql

Question

Suppose, I have the following table T1:
| type | col1 | col2 |
|------|------|------|
| abc | 0 | 0 |
| def | 0 | 3 |
| abc | 3 | 123 |
| def | 0 | 5 |
| def | 2 | 4 |
Periodically, some new values are inserted into T1. I now want to create a trigger, which populates another table T2, depending on the values inserted into T1.
The values to insert into T2 can be calculated using the following pseudo code:
IF col1 = 0 AND col2 = 0
A++
ELSE IF col1 = 0 col2 > 0
B++
ELSE IF col1 > 0
C++
I already created the following trigger:
Create TRIGGER TRI1
ON dbo.T1
FOR INSERT
AS
BEGIN
INSERT INTO dbo.T2
SELECT Sum(CASE WHEN col1 = 0 AND col2 = 0 THEN 1 END) as 'A',
Sum(CASE WHEN col1 = 0 AND col2 > 0 THEN 1 END) as 'B',
Sum(CASE WHEN col1 > 0 THEN 1 END) as 'C'
FROM INSERTED
END
When I test it with:
INSERT INTO dbo.T1 VALUES ('abc',2,3)
INSERT INTO dbo.T1 VALUES ('abc',0,0)
INSERT INTO dbo.T1 VALUES ('def',0,3)
INSERT INTO dbo.T1 VALUES ('abc',0,0)
I get the following output:
| A | B | C |
|------|------|------|
| NULL | NULL | 1 |
| 1 | NULL | NULL |
| NULL | 1 | NULL |
| 1 | NULL | NULL |
But the expected output is only 1 row per insert operation:
| A | B | C |
|---|---|---|
| 2 | 1 | 1 |

Answer 1

You should create a trigger like this,
CREATE TRIGGER TRI1 ON dbo.T1
FOR INSERT
AS
BEGIN
IF EXISTS (
SELECT 1
FROM dbo.T2
)
BEGIN
UPDATE T
SET A = Sum(CASE
WHEN T.col1 = 0
AND T.col2 = 0
THEN 1
ELSE 0
END)
,B = Sum(CASE
WHEN T.col1 = 0
AND T.col2 > 0
THEN 1
ELSE 0
END)
,C = Sum(CASE
WHEN T.col1 > 0
THEN 1
ELSE 0
END)
FROM dbo.t1 T
END
ELSE
BEGIN
INSERT INTO dbo.T2
SELECT Sum(CASE
WHEN T.col1 = 0
AND T.col2 = 0
THEN 1
ELSE 0
END) AS 'A'
,Sum(CASE
WHEN T.col1 = 0
AND T.col2 > 0
THEN 1
ELSE 0
END) AS 'B'
,Sum(CASE
WHEN T.col1 > 0
THEN 1
ELSE 0
END) AS 'C'
FROM dbo.t1 T
END
END