Oracle查询以获取同一表中相关行的先前值

2023年10月29日 182次阅读

我有一张桌子学生,名字和评分年份明智.

Name    Year    Rating

Ram    2016      10
Sam    2016      9
Ram    2014      8
Sam    2012      7

我需要找到员工之前的评级,可能是去年或几年前.

查询应返回以下结果

Name    Cur_rating_year_2016    Prev_rating
Ram               10            8
Sam                9            7

下面是insert和create的脚本

Create table Student (name varchar2(10), year number, rating number  );
insert into student values('Ram' ,2016 ,10);
insert into student values('Sam' ,2016 ,9);
insert into student values('Sam' ,2012 ,7);
insert into student values('Ram' ,2014 ,8);

有没有办法使用选择查询来实现这一目标？

最佳答案 使用LAG分析功能
https://docs.oracle.com/database/122/SQLRF/LAG.htm#SQLRF00652

LAG is an analytic function. It provides access to more than one row
of a table at the same time without a self join. Given a series of
rows returned from a query and a position of the cursor, LAG provides
access to a row at a given physical offset prior to that position.

For the optional offset argument, specify an integer that is greater
than zero. If you do not specify offset, then its default is 1. The
optional default value is returned if the offset goes beyond the scope
of the window. If you do not specify default, then its default is
null.

SELECT stud_name AS name, 
       r_year AS year,
       r_value AS rating,
       lag(r_value, 1, NULL) OVER(PARTITION BY stud_name ORDER BY r_year) AS prev_rating
  FROM stud_r
 ORDER BY stud_name;
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