DECLARE @MyTable TABLE
                (
                    COl1    INT,
                    COl2    INT
        );

SELECT @MyTable.Col1 FROM @MyTable;

UPDATE @MyTable
    SET Co2 = A,Cik2
    FROM Table2 AS A
    WHERE A.Col1 = @MyTable.Col1;

DECLARE @MyTable TABLE
                (
                    COl1    INT,
                    COl2    INT
        );

SELECT MT.Col1 FROM @MyTable AS MT;

UPDATE MT
    SET Co2 = A.Cik2
    FROM @MyTable AS MT
    INNER JOIN Table2 AS A
    WHERE A.Col1 = MT.Col1;

MERGE INTO @MyTable AS Tgt
USING (SELECT Cik2, Col1 FROM dbo.Table2) AS Src
ON Tgt.Col1 = Src.Col1
WHEN MATCHED THEN UPDATE
SET Col1 = Src.Col1;