merge-using-cte-source

CREATE TABLE #src (
    a    int NOT NULL,
    b    numeric(28, 8) NOT NULL,
    PRIMARY KEY (a)
);

INSERT INTO #src VALUES (1, 1234.00), (3, 1340.00);

CREATE TABLE #tgt (
    a    int NOT NULL,
    b    numeric(28, 8) NOT NULL
    PRIMARY KEY (a)
);

INSERT INTO #tgt VALUES (2, 1239.00), (3, 1345.00);

SELECT *
FROM #src AS src
FULL JOIN #tgt AS tgt ON
    src.a=tgt.a;