Full join?

USE tempdb;

CREATE TABLE dbo.Table1(
NUMPAT int NOT NULL,
TRACT int NOT NULL,
ITEMa int NOT NULL
);

CREATE TABLE dbo.Table2(
NUMPAT int NOT NULL,
TRACT int NOT NULL,
ITEMb int NOT NULL
);

INSERT dbo.Table1 VALUES(1, 100, 50);
INSERT dbo.Table1 VALUES(2, 134, 60);
INSERT dbo.Table1 VALUES(5, 200, 30);

INSERT dbo.Table2 VALUES(1, 100, 55);
INSERT dbo.Table2 VALUES(3, 126, 40);
INSERT dbo.Table2 VALUES(4, 140, 70);
INSERT dbo.Table2 VALUES(5, 100, 20);

SELECT 
      COALESCE(T1.NUMPAT, T2.NUMPAT) AS NUMPAT
    , T1.TRACT AS TRACT1
    , T2.TRACT AS TRACT2
    , T1.ITEMa
    , T2.ITEMb
FROM dbo.Table1 AS T1
FULL JOIN dbo.Table2 AS T2
ON T1.NUMPAT = T2.NUMPAT
AND T1.TRACT = T2.TRACT
ORDER BY NUMPAT;

/* Output:

NUMPAT      TRACT1      TRACT2      ITEMa       ITEMb
----------- ----------- ----------- ----------- -----------
1           100         100         50          55
2           134         NULL        60          NULL
3           NULL        126         NULL        40
4           NULL        140         NULL        70
5           NULL        100         NULL        20
5           200         NULL        30          NULL

(6 row(s) affected)

*/

DROP TABLE dbo.Table1, dbo.Table2;