Question

下面是学生表DDL和DML

CREATE TABLE STUDENTS
(
  CLASS NUMBER,
  STUDENT_ROLLNO  NUMBER,
  SUBJECT VARCHAR2(50)
);

INSERT INTO STUDENTS(CLASS, STUDENT_ROLLNO, SUBJECT) VALUES(1, 1,'ENGLISH');
INSERT INTO STUDENTS(CLASS, STUDENT_ROLLNO, SUBJECT) VALUES(1, 1,  'MATHS');
INSERT INTO STUDENTS(CLASS, STUDENT_ROLLNO, SUBJECT) VALUES(1, 1,  'SCIENCE');
INSERT INTO STUDENTS(CLASS, STUDENT_ROLLNO, SUBJECT) VALUES(1, 1,  'ART');
INSERT INTO STUDENTS(CLASS, STUDENT_ROLLNO, SUBJECT) VALUES(1, 2,  'ENGLISH');
INSERT INTO STUDENTS(CLASS, STUDENT_ROLLNO, SUBJECT) VALUES(1, 2,  'MATHS');
INSERT INTO STUDENTS(CLASS, STUDENT_ROLLNO, SUBJECT) VALUES(1, 2,  'FRENCH');
INSERT INTO STUDENTS(CLASS, STUDENT_ROLLNO, SUBJECT) VALUES(1, 2,  'POETRY');
INSERT INTO STUDENTS(CLASS, STUDENT_ROLLNO, SUBJECT) VALUES(1, 3,  'ENGLISH');
INSERT INTO STUDENTS(CLASS, STUDENT_ROLLNO, SUBJECT) VALUES(1, 3,  'MATHS');

现在我需要找到该班的每个学生选择的共同科目。对于这种情况，英语和数学将是结果。

我需要编写查询来获取所需的结果，因为它们是更多的类，结果应该是按类。

感谢。

Answer 1

试试这个

 WITH SUB1 AS (
SELECT  
CLASS,SUBJECT,COUNT(*) NMB  FROM
STUDENTS
GROUP BY CLASS,SUBJECT
),SUB2 AS(
SELECT CLASS, MAX(NMB)MAX_NMB FROM
(SELECT  
CLASS,COUNT(*) NMB  FROM
STUDENTS
GROUP BY CLASS,SUBJECT
)
GROUP BY CLASS
)
SELECT SUB1.CLASS,SUB1.SUBJECT
FROM SUB1
INNER JOIN SUB2
ON SUB1.NMB=SUB2.MAX_NMB  AND SUB1.CLASS=SUB2.CLASS

Answer 2

没有任何自我加入：

SELECT class,
       subject
FROM   (
  SELECT s.*,
         COUNT( DISTINCT student_rollno ) OVER ( PARTITION BY class ) AS num_students
  FROM   students s
)
GROUP BY class, subject
HAVING   COUNT( DISTINCT student_rollno ) = MAX( num_students );

<强>输出：

CLASS SUBJECT
----- -------
    1 ENGLISH
    1 MATHS

Oracle SQL：查找每个班级学生共同学习的科目

2 个答案:

试试这个