如何从表中检索最新数据

Question

目前我正在做一个项目，我需要从一个表中提取最新的数据用于报告目的。下面是示例表结构：-

我使用下面的SQL查询并能够提取数据。

CREATE TABLE COURSE
    ("STUDENT_ID" int, "COURSE_ID" int, "COURSE_NAME" varchar2(31), "COURSE_START_DATE" timestamp)
;

INSERT ALL 
    INTO COURSE ("STUDENT_ID", "COURSE_ID", "COURSE_NAME", "COURSE_START_DATE")
         VALUES (100001, -100, 'C Programming Language', '04-Feb-2019 12:00:00 AM')
    INTO COURSE ("STUDENT_ID", "COURSE_ID", "COURSE_NAME", "COURSE_START_DATE")
         VALUES (100001, -200, 'Java Programming Language', '11-Feb-2019 12:00:00 AM')
    INTO COURSE ("STUDENT_ID", "COURSE_ID", "COURSE_NAME", "COURSE_START_DATE")
         VALUES (100001, -300, 'C# Programming Language', '07-Feb-2019 12:00:00 AM')
    INTO COURSE ("STUDENT_ID", "COURSE_ID", "COURSE_NAME", "COURSE_START_DATE")
         VALUES (100001, 100, 'Data Structure and algorithms', '05-Feb-2019 12:00:00 AM')
    INTO COURSE ("STUDENT_ID", "COURSE_ID", "COURSE_NAME", "COURSE_START_DATE")
         VALUES (100001, 200, 'Computer Graphics', '13-Feb-2019 12:00:00 AM')
    INTO COURSE ("STUDENT_ID", "COURSE_ID", "COURSE_NAME", "COURSE_START_DATE")
         VALUES (100001, 300, 'Networking', '02-Feb-2019 12:00:00 AM')
    INTO COURSE ("STUDENT_ID", "COURSE_ID", "COURSE_NAME", "COURSE_START_DATE")
         VALUES (100002, -300, 'C# Programming Language', '12-Feb-2019 12:00:00 AM')
    INTO COURSE ("STUDENT_ID", "COURSE_ID", "COURSE_NAME", "COURSE_START_DATE")
         VALUES (100002, -400, 'Python Programming Language', '07-Feb-2019 12:00:00 AM')
    INTO COURSE ("STUDENT_ID", "COURSE_ID", "COURSE_NAME", "COURSE_START_DATE")
         VALUES (100002, -500, 'JavaScript Programming Language', '08-Feb-2019 12:00:00 AM')
    INTO COURSE ("STUDENT_ID", "COURSE_ID", "COURSE_NAME", "COURSE_START_DATE")
         VALUES (100002, 100, 'Data Structure and algorithms', '17-Jan-2019 12:00:00 AM')
    INTO COURSE ("STUDENT_ID", "COURSE_ID", "COURSE_NAME", "COURSE_START_DATE")
         VALUES (100002, 300, 'Computer Graphics', '26-Jan-2019 12:00:00 AM')
    INTO COURSE ("STUDENT_ID", "COURSE_ID", "COURSE_NAME", "COURSE_START_DATE")
         VALUES (100002, 400, 'DataBase Management', '10-Jan-2019 12:00:00 AM')
    INTO COURSE ("STUDENT_ID", "COURSE_ID", "COURSE_NAME", "COURSE_START_DATE")
         VALUES (100003, -500, 'JavaScript Programming Language', '07-Feb-2019 12:00:00 AM')
    INTO COURSE ("STUDENT_ID", "COURSE_ID", "COURSE_NAME", "COURSE_START_DATE")
         VALUES (100003, -600, 'SQL', '13-Feb-2019 12:00:00 AM')
    INTO COURSE ("STUDENT_ID", "COURSE_ID", "COURSE_NAME", "COURSE_START_DATE")
         VALUES (100003, -200, 'Java Programming Language', '17-Jan-2019 12:00:00 AM')
    INTO COURSE ("STUDENT_ID", "COURSE_ID", "COURSE_NAME", "COURSE_START_DATE")
         VALUES (100003, 300, 'Networking', '04-Feb-2019 12:00:00 AM')
    INTO COURSE ("STUDENT_ID", "COURSE_ID", "COURSE_NAME", "COURSE_START_DATE")
         VALUES (100003, 400, 'DataBase Management', '05-Jan-2019 12:00:00 AM')
    INTO COURSE ("STUDENT_ID", "COURSE_ID", "COURSE_NAME", "COURSE_START_DATE")
         VALUES (100003, 600, 'Cryptography', '18-Jan-2019 12:00:00 AM')
SELECT * FROM dual
;

SELECT STUDENT_ID
,COURSE_ID
,COURSE_NAME
,COURSE_START_DATE
  FROM (
SELECT 
ROW_NUMBER() OVER(PARTITION BY STUDENT_ID ORDER BY COURSE_START_DATE DESC) AS ROW_NUM
,STUDENT_ID
,COURSE_ID
,COURSE_NAME
,COURSE_START_DATE
  FROM
COURSE
WHERE COURSE_ID  0) TEMP1 WHERE TEMP1.ROW_NUM = 1;

但问题是真正的表非常大。大约有85k行，这个查询需要一些时间。还有其他更好的方法吗。我正在使用Oracle 11g R2。请建议

这是SQLfiddle链接http://sqlfiddle.com/#!4/b3fe1/8

Answer 1

您可以使用查询并将符号（课程id）添加到分区：

查询：

SELECT STUDENT_ID
     , COURSE_ID
     , COURSE_NAME
     , COURSE_START_DATE
FROM (
  SELECT ROW_NUMBER() OVER (
           PARTITION BY STUDENT_ID, SIGN( COURSE_ID )
           ORDER BY COURSE_START_DATE DESC
         ) AS ROW_NUM
       , STUDENT_ID
       , COURSE_ID
       , COURSE_NAME
       , COURSE_START_DATE
  FROM   COURSE
  WHERE COURSE_ID != 0
)
WHERE  ROW_NUM = 1;

输出：

STUDENT_ID | COURSE_ID | COURSE_NAME               | COURSE_START_DATE           
---------: | --------: | :------------------------ | :---------------------------
    100001 |      -200 | Java Programming Language | 11-FEB-19 12.00.00.000000 AM
    100001 |       200 | Computer Graphics         | 13-FEB-19 12.00.00.000000 AM
    100002 |      -300 | C# Programming Language   | 12-FEB-19 12.00.00.000000 AM
    100002 |       300 | Computer Graphics         | 26-JAN-19 12.00.00.000000 AM
    100003 |      -600 | SQL                       | 13-FEB-19 12.00.00.000000 AM
    100003 |       300 | Networking                | 04-FEB-19 12.00.00.000000 AM

db

Answer 2

将CTE与row_number结合

with pro as 
(
select t1.*, row_number() over(partition by student_id order by course_start_date desc) rn
from course 
where course_id > 0 -- programming
)
, nonpro as 
(
select t1.*, row_number() over(partition by student_id order by course_start_date desc) rn
from course 
where course_id < 0 -- non-programming
)
select *
from pro
where rn = 1
union
select *
from nonpro
where rn = 1

Answer 3

您可以在下面尝试-您需要添加按学生ID划分的分区，当课程ID为

SELECT STUDENT_ID,COURSE_ID,COURSE_NAME,COURSE_START_DATE
FROM 
(
  SELECT 
  ROW_NUMBER() OVER(PARTITION BY STUDENT_ID,case when course_id<0 then 1 else 2 end order by COURSE_START_DATE DESC) AS ROW_NUM
, STUDENT_ID,COURSE_ID,COURSE_NAME,COURSE_START_DATE FROM COURSE
 )TEMP1 WHERE TEMP1.ROW_NUM = 1;