Skip duplicates while importing data into SQL server

You can use the T-SQL MERGE statement to do this. It will match the row set being imported with your HallSeat table. If the row doesn't exist, it will insert a new row. If the row does exist and there are differences, it can update it.

(You might not want to do the delete action, but I have included it for completeness.)

See Books Online > MERGE (Transact-SQL) -- https://msdn.microsoft.com/en-GB/library/bb510625.aspx

To demonstrate this, first create two tables.

CREATE TABLE dbo.HallSeat
(
    HallGroupID int NOT NULL,
    ShowSeatID int NOT NULL,
    Color nvarchar(15) NOT NULL,
    Price int NOT NULL,
    SeatRow int NOT NULL,
    SeatNumber int NOT NULL,
    IsReserved bit NOT NULL,
    CONSTRAINT PK_HallSeat PRIMARY KEY CLUSTERED (HallGroupID, ShowSeatID)
);

CREATE TABLE dbo.ImportHallSeat
(
    HallGroupID int NOT NULL,
    ShowSeatID int NOT NULL,
    Color nvarchar(15) NOT NULL,
    Price int NOT NULL,
    SeatRow int NOT NULL,
    SeatNumber int NOT NULL,
    IsReserved bit NOT NULL,
    CONSTRAINT PK_ImportHallSeat PRIMARY KEY CLUSTERED (HallGroupID, ShowSeatID)
);

Then import the XML data file into the ImportHallSeat table:

-- Read the XML data file to be imported
DECLARE @xml xml;
SELECT @xml = x.a
    FROM OPENROWSET(BULK 'F:\Work\Data.xml', SINGLE_BLOB) AS x(a);

TRUNCATE TABLE dbo.ImportHallSeat;

INSERT INTO dbo.ImportHallSeat(HallGroupID, ShowSeatID, Color, Price, SeatRow, SeatNumber, IsReserved)
    SELECT T.C.value('HallGroupID[1]', 'int') AS 'HallGroupID',
            T.C.value('ShowSeatID[1]', 'int') AS 'ShowSeatID',
            T.C.value('Color[1]', 'nvarchar(15)') AS 'Color',
            T.C.value('Price[1]', 'money') AS 'Price',
            T.C.value('SeatRow[1]', 'int') AS 'SeatRow',
            T.C.value('SeatNumber[1]', 'int') AS 'SeatNumber',
            T.C.value('IsReserved[1]', 'bit') AS 'IsReserved'
        FROM @xml.nodes(N'/Filharmonija/Hall/HallGroup/HallSeat') as T(C);

Then we can update the HallSeat table with the data being imported:

MERGE
    INTO dbo.HallSeat AS H
    USING dbo.ImportHallSeat AS I
    ON I.HallGroupID = H.HallGroupID AND I.ShowSeatID = H.ShowSeatID
    WHEN MATCHED AND H.Color <> I.Color AND H.Price <> I.Price
        THEN UPDATE SET H.Color = I.Color, H.Price = I.Price
    WHEN NOT MATCHED BY TARGET
        THEN INSERT (HallGroupID, ShowSeatID, Color, Price, SeatRow, SeatNumber, IsReserved)
            VALUES (I.HallGroupID, I.ShowSeatID, I.Color, I.Price, I.SeatRow, I.SeatNumber, I.IsReserved)
    WHEN NOT MATCHED BY SOURCE
        THEN DELETE;

Display the data that has been imported into the HallSeat table:

SELECT *
    FROM dbo.HallSeat;