sql server generate merge statement

CREATE FUNCTION system.GenerateMERGE
(
    @TABLESCHEMA    NAME,
    @TABLENAME      NAME
)
RETURNS VARCHAR(MAX)
AS
BEGIN
    DECLARE @RV     VARCHAR(MAX) = ''
    DECLARE @CRLF   VARCHAR(2) = CHAR(13)+CHAR(10)
    DECLARE @TAB    VARCHAR(1) = CHAR(9)

    DECLARE @IDENT  BIT = (SELECT OBJECTPROPERTY(OBJECT_ID(@TABLESCHEMA+'.'+@TABLENAME), 'TableHasIdentity'))

    IF @IDENT != 0 SELECT @RV = 'SET IDENTITY_INSERT '+@TABLESCHEMA+'.'+@TABLENAME+' ON'+@CRLF

    SELECT @RV = @RV + 'MERGE INTO '+@TABLESCHEMA+'.'+@TABLENAME+' D'+@CRLF+
                 'USING (<enter source query here>) S'+@CRLF+'ON '

    SELECT @RV = @RV+'S.'+PK.TABLE_FIELD+' = D.'+TABLE_FIELD+' AND '
    FROM system.PKCOLS PK
    WHERE PK.TABLE_SCHEMA = @TABLESCHEMA AND PK.TABLE_NAME = @TABLENAME
    ORDER BY PK.ORDINAL_POSITION
    SELECT @RV = LEFT(@RV, LEN(@RV) - 4)+@CRLF

    SELECT @RV = @RV+'WHEN MATCHED UPDATE SET'+@CRLF
    SELECT @RV = @RV+@TAB+C.COLUMN_NAME+' = S.'+C.COLUMN_NAME+','+@CRLF
    FROM INFORMATION_SCHEMA.COLUMNS C
    LEFT JOIN system.PKCOLS PK ON PK.TABLE_SCHEMA = C.TABLE_SCHEMA AND PK.TABLE_NAME = C.TABLE_NAME AND PK.TABLE_FIELD = C.COLUMN_NAME
    WHERE C.TABLE_SCHEMA = @TABLESCHEMA AND C.TABLE_NAME = @TABLENAME AND PK.TABLE_FIELD IS NULL
            AND COLUMNPROPERTY(OBJECT_ID(@TABLESCHEMA+'.'+@TABLENAME), C.COLUMN_NAME, 'IsComputed') = 0
    ORDER BY C.ORDINAL_POSITION
    SELECT @RV = LEFT(@RV, LEN(@RV) - 3)+@CRLF

    SELECT @RV = @RV+'WHEN NOT MATCHED'+@CRLF+@TAB+'INSERT ('
    SELECT @RV = @RV+C.COLUMN_NAME+', '
    FROM INFORMATION_SCHEMA.COLUMNS C
    LEFT JOIN system.PKCOLS PK ON PK.TABLE_SCHEMA = C.TABLE_SCHEMA AND PK.TABLE_NAME = C.TABLE_NAME AND PK.TABLE_FIELD = C.COLUMN_NAME
    WHERE C.TABLE_SCHEMA = @TABLESCHEMA AND C.TABLE_NAME = @TABLENAME
            AND COLUMNPROPERTY(OBJECT_ID(@TABLESCHEMA+'.'+@TABLENAME), C.COLUMN_NAME, 'IsComputed') = 0
    ORDER BY C.ORDINAL_POSITION
    SELECT @RV = LEFT(@RV, LEN(@RV) - 1)+')'+@CRLF+@TAB+'VALUES ('

    SELECT @RV = @RV+'S.'+C.COLUMN_NAME+', '
    FROM INFORMATION_SCHEMA.COLUMNS C
    LEFT JOIN system.PKCOLS PK ON PK.TABLE_SCHEMA = C.TABLE_SCHEMA AND PK.TABLE_NAME = C.TABLE_NAME AND PK.TABLE_FIELD = C.COLUMN_NAME
    WHERE C.TABLE_SCHEMA = @TABLESCHEMA AND C.TABLE_NAME = @TABLENAME
            AND COLUMNPROPERTY(OBJECT_ID(@TABLESCHEMA+'.'+@TABLENAME), C.COLUMN_NAME, 'IsComputed') = 0
    ORDER BY C.ORDINAL_POSITION
    SELECT @RV = LEFT(@RV, LEN(@RV) - 1)+');'+@CRLF

    IF @IDENT != 0 SELECT @RV = @RV+'SET IDENTITY_INSERT '+@TABLESCHEMA+'.'+@TABLENAME+' OFF'+@CRLF

    RETURN @RV
END
GO