Select a.id_student,ISNULL(b.score,0) AS score
From Student a
Left Outer Join score b on a.id_student=b.id_student 
Where[color=#FF0000] b.id_student Is Null [/color]or b.score<60

------解决方案--------------------

SQL code

IF EXISTS (SELECT 1 FROM SYSOBJECTS WHERE name = 'Student')
BEGIN
    DROP TABLE Student
END
GO
CREATE TABLE Student
(
    id_student INT,
    grade INT
)
GO
IF EXISTS (SELECT 1 FROM SYSOBJECTS WHERE name = 'score')
BEGIN
    DROP TABLE score
END
GO
CREATE TABLE score
(
    id_score INT,
    id_student INT,
    score INT
)
GO
INSERT INTO Student
SELECT 1,1 UNION
SELECT 2,1 UNION
SELECT 3,1 UNION
SELECT 4,1 

INSERT INTO score
SELECT 1,1,70 UNION
SELECT 2,3,57 UNION
SELECT 3,4,10 

SELECT A.id_student,score
FROM Student AS A LEFT OUTER JOIN score AS B ON A.id_student = B.id_student
WHERE ISNULL(score,0) < 60

id_student    score
2    NULL
3    57
4    10