What is wrong with my trigger? No results are inserted - sql-server

Question

The trigger below select ID's from one table (employeeInOut), sums int's in a column in that table matching all ID's, and is supposed to insert these in another table (monthlyHours). I can't figure out if this is a syntax problem (nothing shows up in intellisense), and all it says is trigger executed successfully - nothing is inserted.
Trigger ->
GO
CREATE TRIGGER empTotalsHoursWorked
ON employeeInOut
FOR INSERT, DELETE, UPDATE
AS
BEGIN
INSERT INTO monthlyHours(employeeID, monthlyHours)
SELECT (SELECT employeeID FROM employeeInOut),
SUM(dailyHours) AS monthlyHours
FROM employeeInOut
WHERE employeeInOut.employeeID=(SELECT employeeID FROM monthlyHours)
END
GO
I have re-worked this trigger many times and this is the one with no errors, however nothing is inserted, and results seem to be nothing. Any advice, answers please appreciated.

Answer 1

Going with a couple of assumptions here one being that monthlyHours table contains employeeID and monthlyhours.
With that being said I think you are going to need multiple triggers depending on the action. Below is an example based on insert into the employeeInOut table
GO
CREATE TRIGGER empTotalsHoursWorked
ON employeeInOut
AFTER INSERT
AS
BEGIN
DECLARE #employeeID INT
DECLARE #monthlyHours INT
SELECT #employeeID = INSERTED.employeeID
FROM INSERTED
SELECT #monthlyHours = SUM(dailyHours)
FROM employeeInOut
WHERE employeeInOut.employeeID = #employeeID
INSERT INTO monthlyHours(employeeID,monthlyHours)
values (#employeeID, #monthlyHours)
END
GO
This will insert a new row of course. You may want to modify this to update the row if the row already exists in the monthlyHours table for that employee.

Answer 2

I would really advise against a trigger for a simple running total like this, your best option would be to create a view. Something like:
CREATE VIEW dbo.MonthlyHours
AS
SELECT EmployeeID,
monthlyHours = SUM(dailyHours)
FROM dbo.employeeInOut
GROUP BY EmployeeID;
GO
Then you can access it in the same way as your table:
SELECT *
FROM dbo.MonthlyHours;
If you are particularly worried about performance, then you can always index the view:
CREATE VIEW dbo.MonthlyHours
WITH SCHEMABINDING
AS
SELECT EmployeeID,
monthlyHours = SUM(dailyHours),
RecordCount = COUNT_BIG(*)
FROM dbo.employeeInOut
GROUP BY EmployeeID;
GO
CREATE UNIQUE CLUSTERED INDEX UQ_MonthlyHours__EmployeeID ON dbo.MonthlyHours(EmployeeID);
Now whenever you add or remove records from employeeInOut SQL Server will automatically update the clustered index for the view, you just need to use the WITH (NOEXPAND) query hint to ensure that you aren't running the query behind the view:
SELECT *
FROM dbo.MonthlyHours WITH (NOEXPAND);
Finally, based on the fact the table is called monthly hours, I am guessing it should be by month, as such I assume you also have a date field in employeeInOut, in which case your view might be more like:
CREATE VIEW dbo.MonthlyHours
WITH SCHEMABINDING
AS
SELECT EmployeeID,
FirstDayOfMonth = DATEADD(MONTH, DATEDIFF(MONTH, 0, [YourDateField]), 0),
monthlyHours = SUM(dailyHours),
RecordCount = COUNT_BIG(*)
FROM dbo.employeeInOut
GROUP BY EmployeeID, DATEADD(MONTH, DATEDIFF(MONTH, 0, [YourDateField]), 0);
GO
CREATE UNIQUE CLUSTERED INDEX UQ_MonthlyHours__EmployeeID_FirstDayOfMonth
ON dbo.MonthlyHours(EmployeeID, FirstDayOfMonth);
And you can use the view in the same way described above.
ADDENDUM
For what it is worth, for your trigger to work properly you need to consider all cases:
Inserting a record where that employee already exists in MonthlyHours (Update existing).
Inserting a record where that employee does not exist in MonthlyHours (insert new).
Updating a record (update existing)
Deleting a record (update existing, or delete)
To handle all of these cases you can use MERGE:
CREATE TRIGGER empTotalsHoursWorked
ON employeeInOut
FOR INSERT, DELETE, UPDATE
AS
BEGIN
WITH ChangesToMake AS
( SELECT EmployeeID, SUM(dailyHours) AS MonthlyHours
FROM ( SELECT EmployeeID, dailyHours
FROM Inserted
UNION ALL
SELECT EmployeeID, -dailyHours
FROM deleted
) AS t
GROUP BY EmployeeID
)
MERGE INTO monthlyHours AS m
USING ChangesToMake AS c
ON c.EmployeeID = m.EmployeeID
WHEN MATCHED THEN UPDATE
SET MonthlyHours = c.MonthlyHours
WHEN NOT MATCHED BY TARGET THEN
INSERT (EmployeeID, MonthlyHours)
VALUES (c.EmployeeID, c.MonthlyHours)
WHEN NOT MATCHED BY SOURCE THEN
DELETE;
END
GO