SQL Server 2019

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DECLARE @Overtime TABLE (
    EmployeeId      INT,
    OvertimeDate    DATE,
    HourMargin      TIME,
    OvertimePoint   INT
)

DECLARE @OLC TABLE (
    EmployeeId      INT,
    OLCDate         DATE,
    OLC             INT,
    Trip            INT
)

INSERT INTO @Overtime VALUES (1, '2020-07-01', '05:00:00', 15)
INSERT INTO @Overtime VALUES (1, '2020-07-02', '03:00:00', 9)
INSERT INTO @Overtime VALUES (2, '2020-07-01', '01:00:00', 3)
INSERT INTO @Overtime VALUES (2, '2020-07-03', '03:00:00', 9)
INSERT INTO @Overtime VALUES (3, '2020-07-06', '03:00:00', 9)
INSERT INTO @Overtime VALUES (3, '2020-07-07', '01:00:00', 3)

INSERT INTO @OLC VALUES (1, '2020-07-01', 2, 0)
INSERT INTO @OLC VALUES (3, '2020-07-13', 3, 6)

SELECT
    OT.EmployeeId,
    CONVERT(TIME, DATEADD(MS, SUM(DATEDIFF(MS, '00:00:00.000', OT.HourMargin)), '00:00:00.000')) AS TotalMargin,
    SUM(OT.OvertimePoint) AS TotalPoint,
    COALESCE(SUM(OLC.OLC), 0) AS TotalOLC,
    COALESCE(SUM(OLC.Trip), 0) AS TotalTrip
FROM @Overtime OT
LEFT JOIN @OLC OLC ON OLC.EmployeeId = OT.EmployeeId
GROUP BY OT.EmployeeId

EmployeeId	TotalMargin	TotalPoint	TotalOLC	TotalTrip
1	08:00:00.0000000	24	4	0
2	04:00:00.0000000	12	0	0
3	04:00:00.0000000	12	6	12

Warning: Null value is eliminated by an aggregate or other SET operation.

Msg 1087 Level 15 State 2 Line 7
Must declare the table variable "@Overtime".