如何在 Oracle 中为查询结果分配排名?
oraclesoftware & codingprogramming
问题陈述:
您想要分配一个数字/排名来表示它们在结果中的位置。
解决方案:
Oracle 提供 RANK 分析函数来为结果集中的行生成排名数字。为了演示，我们将按费用对学生进行排名，从最高费用开始。以下 SELECT 语句使用排名函数来分配这些值。
示例
SELECT student_id, first_name, last_name, fees, RANK() OVER (ORDER BY fees DESC) AS rnk FROM students;
输出
| student_id | first_name | last_name | fees | rnk |
| 100 | SMITH | JAMES | 24000 | 1 |
| 101 | JOHNSON | JOHN | 17000 | 2 |
| 102 | WILLIAMS | ROBERT | 17000 | 2 |
| 108 | RODRIGUEZ | JOSEPH | 12008 | 4 |
| 103 | BROWN | MICHAEL | 9000 | 5 |
| 109 | WILSON | THOMAS | 9000 | 5 |
| 110 | MARTINEZ | CHRISTOPHER | 8200 | 7 |
| 112 | TAYLOR | PAUL | 7800 | 8 |
| 111 | ANDERSON | DANIEL | 7700 | 9 |
| 113 | THOMAS | MARK | 6900 | 10 |
| 104 | JONES | WILLIAM | 6000 | 11 |
| 105 | MILLER | DAVID | 4800 | 12 |
| 106 | DAVIS | RICHARD | 4800 | 12 |
| 107 | GARCIA | CHARLES | 4200 | 14 |
RANK 的行为类似于任何其他分析函数，在非分析处理完成后对结果集进行第二次操作。在上述 SQL 中，结果按费用降序处理，并从 1 开始计算结果的排名值。
一对学生的学费相似，均为 12008，排名为 4。这称为稀疏排名，其中相同的值排名相同。这可能是也可能不是您想要的结果，具体取决于您的要求，因为缺少一些排名。
稀疏排名的替代方法称为密集排名。我们将使用致密排名函数观察结果。
示例
SELECT student_id, first_name, last_name, fees, dense_rank() OVER (ORDER BY fees DESC) AS rnk FROM students
输出
| student_id | first_name | last_name | fees | rnk |
| 100 | SMITH | JAMES | 24000 | 1 |
| 101 | JOHNSON | JOHN | 17000 | 2 |
| 102 | WILLIAMS | ROBERT | 17000 | 2 |
| 108 | RODRIGUEZ | JOSEPH | 12008 | 3 |
| 103 | BROWN | MICHAEL | 9000 | 4 |
| 109 | WILSON | THOMAS | 9000 | 4 |
| 110 | MARTINEZ | CHRISTOPHER | 8200 | 5 |
| 112 | TAYLOR | PAUL | 7800 | 6 |
| 111 | ANDERSON | DANIEL | 7700 | 7 |
| 113 | THOMAS | MARK | 6900 | 8 |
| 104 | JONES | WILLIAM | 6000 | 9 |
| 105 | MILLER | DAVID | 4800 | 10 |
| 106 | DAVIS | RICHARD | 4800 | 10 |
| 107 | GARCIA | CHARLES | 4200 | 11 |
我们现在可以看到缺失的连续排名值。
数据准备:用于该问题的数据如下所示。
示例
DROP TABLE students; COMMIT; CREATE TABLE students ( student_id NUMBER(6) , first_name VARCHAR2(20) , last_name VARCHAR2(25) , email VARCHAR2(40) , phone_number VARCHAR2(20) , join_date DATE , class_id VARCHAR2(20) , fees NUMBER(8,2) , professor_id NUMBER(6) , department_id NUMBER(4) ) ;
示例
CREATE UNIQUE INDEX stu_id_pk ON students (student_id) ;
INSERT INTO students VALUES (100,'SMITH','JAMES','SMITH.JAMES@notreal.com','111.111.1245',TO_DATE('17-06-2003','DD-MM-YYYY'),'INS_CHAIRMAN',24000,NULL,NULL);
INSERT INTO students VALUES (101,'JOHNSON','JOHN','JOHNSON.JOHN@notreal.com','111.111.1246',TO_DATE('21-09-2005','DD-MM-YYYY'),'INS_VP',17000,100,90);
INSERT INTO students VALUES (102,'WILLIAMS','ROBERT','WILLIAMS.ROBERT@notreal.com','111.111.1247',TO_DATE('13-01-2001','DD-MM-YYYY'),'INS_VP',17000,100,90);
INSERT INTO students VALUES (103,'BROWN','MICHAEL','BROWN.MICHAEL@notreal.com','111.111.1248',TO_DATE('03-01-2006','DD-MM-YYYY'),'INS_STAFF',9000,102,60);
INSERT INTO students VALUES (104,'JONES','WILLIAM','JONES.WILLIAM@notreal.com','111.111.1249',TO_DATE('21-05-2007','DD-MM-YYYY'),'INS_STAFF',6000,103,60);
INSERT INTO students VALUES (105,'MILLER','DAVID','MILLER.DAVID@notreal.com','111.111.1250',TO_DATE('25-06-2005','DD-MM-YYYY'),'INS_STAFF',4800,103,60);
INSERT INTO students VALUES (106,'DAVIS','RICHARD','DAVIS.RICHARD@notreal.com','111.111.1251',TO_DATE('05-02-2006','DD-MM-YYYY'),'INS_STAFF',4800,103,60);
INSERT INTO students VALUES (107,'GARCIA','CHARLES','GARCIA.CHARLES@notreal.com','111.111.1252',TO_DATE('07-02-2007','DD-MM-YYYY'),'INS_STAFF',4200,103,60);
INSERT INTO students VALUES (108,'RODRIGUEZ','JOSEPH','RODRIGUEZ.JOSEPH@notreal.com','111.111.1253',TO_DATE('17-08-2002','DD-MM-YYYY'),'CL_PHY',12008,101,100);
INSERT INTO students VALUES (109,'WILSON','THOMAS','WILSON.THOMAS@notreal.com','111.111.1254',TO_DATE('16-08-2002','DD-MM-YYYY'),'CL_MATH',9000,108,100);
INSERT INTO students VALUES (110,'MARTINEZ','CHRISTOPHER','MARTINEZ.CHRISTOPHER@notreal.com','111.111.1255',TO_DATE('28-09-2005','DD-MM-YYYY'),'CL_MATH',8200,108,100);
INSERT INTO students VALUES (111,'ANDERSON','DANIEL','ANDERSON.DANIEL@notreal.com','111.111.1256',TO_DATE('30-09-2005','DD-MM-YYYY'),'CL_MATH',7700,108,100);
INSERT INTO students VALUES (112,'TAYLOR','PAUL','TAYLOR.PAUL@notreal.com','111.111.1257',TO_DATE('07-03-2006','DD-MM-YYYY'),'CL_MATH',7800,108,100);
INSERT INTO students VALUES (113,'THOMAS','MARK','THOMAS.MARK@notreal.com','111.111.1258',TO_DATE('07-12-2007','DD-MM-YYYY'),'CL_MATH',6900,108,100);
COMMIT;
