How can i create trigger using GROUP BY - sql-server

Question

I want to create a trigger after insert and update which calculate the sum of values in multiple rows and set the sum in [Target_Cummlative]. I try the following code but that causes this error:
Msg 156, Level 15, State 1, Procedure target_cummlative, Line 13
Incorrect syntax near the keyword 'FROM
My code:
CREATE TRIGGER [dbo].[target_cummlative]
ON [dbo].[Appointments]
AFTER insert, UPDATE
AS
BEGIN
IF TRIGGER_NESTLEVEL() > 1
RETURN
UPDATE T1
SET t1.[Target_Cummlative] = SUM(ISNULL(CAST([TARGET] AS FLOAT), 0)
FROM [Appointments] T1
INNER JOIN inserted i ON T1.[UniqueId] = i.[UniqueId]
GROUP BY CONVERT(VARCHAR(10), t1.[StartDate], 111), t1.[ResourceId]
END
Here is what i have currently, as you can see Target cummlative is null
Id StartDate Location ResourceId TARGET Target_Cummlative
1381 2019-07-22 07:00:00 41051 1 20 NULL
1382 2019-07-22 08:00:00 41051 1 20 NULL
1383 2019-07-22 09:15:00 41051 1 15 NULL
1384 2019-07-22 10:00:00 41051 1 20 NULL
1385 2019-07-22 11:00:00 41051 1 20 NULL
1386 2019-07-22 12:30:00 41051 1 8 NULL
I want set the sum the values in TARGET column and update Target cummlative as
Id StartDate Location ResourceId TARGET Target_Cummlative
1381 2019-07-22 07:00:00 41051 1 20 103
1382 2019-07-22 08:00:00 41051 1 20 103
1383 2019-07-22 09:15:00 41051 1 15 103
1384 2019-07-22 10:00:00 41051 1 20 103
1385 2019-07-22 11:00:00 41051 1 20 103
1386 2019-07-22 12:30:00 41051 1 8 103

Answer 1

If possible - I'd advice against storing cumulative data in the same table, if possible - better create a separate one to store aggregated information.
In any case - your issue is missing parenthesis in SET clause.
CREATE TRIGGER [dbo].[target_cumulative]
ON [dbo].[Appointments]
AFTER insert, UPDATE
AS
BEGIN
IF TRIGGER_NESTLEVEL() > 1
RETURN
UPDATE T1
SET T1.[Target_Cumulative] = SUM(ISNULL(CAST([TARGET] AS FLOAT), 0))
FROM dbo.Appointments AS T1
INNER JOIN inserted AS ION I.UniqueId = T1.UniqueId
GROUP BY CONVERT(DATE, T1.StartDate), T1.ResourceId;
END;
Oh - and there's typo in cummlative, it should be cumulative