【Oracle】oracle的LAG和LEAD分析函数-阿里云开发者社区

【Oracle】oracle的LAG和LEAD分析函数

2016-04-13 1689

版权

本文内容由阿里云实名注册用户自发贡献，版权归原作者所有，阿里云开发者社区不拥有其著作权，亦不承担相应法律责任。具体规则请查看《阿里云开发者社区用户服务协议》和《阿里云开发者社区知识产权保护指引》。如果您发现本社区中有涉嫌抄袭的内容，填写侵权投诉表单进行举报，一经查实，本社区将立刻删除涉嫌侵权内容。

简介：

Lag和Lead函数可以在一次查询中取出同一字段的前N行的数据和后N行的值。这种操作可以使用对相同表的表连接来实现，不过使用LAG和LEAD有更高的效率。

lag的语法如下：

lead的语法如下：

lead 和lag 的语法类似以下以lag为例进行讲解！

lag(exp_str,offset,defval) over()

exp_str 是要做对比的字段

offset 是exp_str字段的偏移量比如说 offset 为2 则拿exp_str的第一行和第三行对比，第二行和第四行，依次类推，offset的默认值为1！

defval是当该函数无值可用的情况下返回的值。Lead函数的用法类似。

以下是lag和lead的例子

SCOTT@yangdb> set pagesize 10000
SCOTT@yangdb> select ename,job,sal ,lag(sal) over(order by sal) last_sal from emp;
ENAME      JOB              SAL   LAST_SAL
---------- --------- ---------- ----------
SMITH      CLERK            800 --此时没有设置default 值则为空值
JAMES      CLERK            950        800
ADAMS      CLERK           1100        950
WARD       SALESMAN        1250       1100
MARTIN     SALESMAN        1250       1250
MILLER     CLERK           1300       1250
TURNER     SALESMAN        1500       1300
ALLEN      SALESMAN        1600       1500
CLARK      MANAGER         2450       1600
BLAKE      MANAGER         2850       2450
JONES      MANAGER         2975       2850
SCOTT      ANALYST         3000       2975
FORD       ANALYST         3000       3000
KING       PRESIDENT       5000       3000
14 rows selected.
设置了default 值之后第一行对应的值为500

SCOTT@yangdb> select ename,job,sal ,lag(sal,1,500) over(order by sal) last_sal from emp;
ENAME      JOB              SAL   LAST_SAL
---------- --------- ---------- ----------
SMITH      CLERK            800        500
JAMES      CLERK            950        800
ADAMS      CLERK           1100        950
WARD       SALESMAN        1250       1100
MARTIN     SALESMAN        1250       1250
MILLER CLERK           1300       1250
TURNER     SALESMAN        1500       1300
ALLEN      SALESMAN        1600       1500
CLARK      MANAGER         2450       1600
BLAKE      MANAGER         2850       2450
JONES      MANAGER         2975       2850
SCOTT      ANALYST         3000       2975
FORD       ANALYST         3000       3000
KING       PRESIDENT       5000       3000
14 rows selected.

指定offset的值为2时
SCOTT@yangdb> select ename,job,sal ,lag(sal,2) over(order by sal) last_sal from emp;
ENAME      JOB              SAL   LAST_SAL
---------- --------- ---------- ----------
SMITH      CLERK            800
JAMES      CLERK            950
ADAMS      CLERK           1100        800
WARD       SALESMAN        1250        950
MARTIN     SALESMAN        1250       1100
MILLER     CLERK           1300       1250
TURNER     SALESMAN        1500       1250
ALLEN      SALESMAN        1600       1300
CLARK      MANAGER         2450       1500
BLAKE      MANAGER         2850       1600
JONES      MANAGER         2975       2450
SCOTT      ANALYST         3000       2850
FORD       ANALYST         3000       2975
KING       PRESIDENT       5000       3000
14 rows selected.

offset的值为3
SCOTT@yangdb> select ename,job,sal ,lag(sal,3) over(order by sal) last_sal from emp;
ENAME      JOB              SAL   LAST_SAL
---------- --------- ---------- ----------
SMITH      CLERK            800
JAMES      CLERK            950
ADAMS      CLERK           1100
WARD       SALESMAN        1250        800
MARTIN     SALESMAN        1250        950
MILLER     CLERK           1300       1100
TURNER     SALESMAN        1500       1250
ALLEN      SALESMAN        1600       1250
CLARK      MANAGER         2450       1300
BLAKE      MANAGER         2850       1500
JONES      MANAGER         2975       1600
SCOTT      ANALYST         3000       2450
FORD       ANALYST         3000       2850
KING       PRESIDENT       5000       2975
14 rows selected.

使用lead分析函数
SCOTT@yangdb> select ename,job,sal ,lead(sal) over(order by sal) last_sal from emp;
ENAME      JOB              SAL   LAST_SAL
---------- --------- ---------- ----------
SMITH      CLERK            800        950
JAMES      CLERK            950       1100
ADAMS      CLERK           1100       1250
WARD       SALESMAN        1250       1250
MARTIN     SALESMAN        1250       1300
MILLER     CLERK           1300       1500
TURNER     SALESMAN        1500       1600
ALLEN      SALESMAN        1600       2450
CLARK      MANAGER         2450       2850
BLAKE      MANAGER         2850       2975
JONES      MANAGER         2975       3000
SCOTT      ANALYST         3000       3000
FORD       ANALYST         3000       5000
KING       PRESIDENT       5000
14 rows selected.
SCOTT@yangdb> select ename,job,sal ,lead(sal,1) over(order by sal) last_sal from emp;
ENAME      JOB              SAL   LAST_SAL
---------- --------- ---------- ----------
SMITH      CLERK            800        950
JAMES      CLERK            950       1100
ADAMS      CLERK           1100       1250
WARD       SALESMAN        1250       1250
MARTIN     SALESMAN        1250       1300
MILLER     CLERK           1300       1500
TURNER     SALESMAN        1500       1600
ALLEN      SALESMAN        1600       2450
CLARK      MANAGER         2450       2850
BLAKE      MANAGER         2850       2975
JONES      MANAGER         2975       3000
SCOTT      ANALYST         3000       3000
FORD       ANALYST         3000       5000
KING       PRESIDENT       5000
14 rows selected.

SCOTT@yangdb> select ename,job,sal ,lead(sal,2) over(order by sal) last_sal from emp;
ENAME      JOB              SAL   LAST_SAL
---------- --------- ---------- ----------
SMITH      CLERK            800       1100
JAMES      CLERK            950       1250
ADAMS      CLERK           1100       1250
WARD       SALESMAN        1250       1300
MARTIN     SALESMAN        1250       1500
MILLER     CLERK           1300       1600
TURNER     SALESMAN        1500       2450
ALLEN      SALESMAN        1600       2850
CLARK      MANAGER         2450       2975
BLAKE      MANAGER         2850       3000
JONES      MANAGER         2975       3000
SCOTT      ANALYST         3000       5000
FORD       ANALYST         3000
KING       PRESIDENT       5000
SCOTT@yangdb> select ename,job,sal ,lead(sal,3) over(order by sal) last_sal from emp;
ENAME      JOB              SAL   LAST_SAL
---------- --------- ---------- ----------
SMITH      CLERK            800       1250
JAMES      CLERK            950       1250
ADAMS      CLERK           1100       1300
WARD       SALESMAN        1250       1500
MARTIN     SALESMAN        1250       1600
MILLER     CLERK           1300       2450
TURNER     SALESMAN        1500       2850
ALLEN      SALESMAN        1600       2975
CLARK      MANAGER         2450       3000
BLAKE      MANAGER         2850       3000
JONES      MANAGER         2975       5000
SCOTT      ANALYST         3000
FORD       ANALYST         3000
KING       PRESIDENT       5000
14 rows selected.

lead 的offset N 是以记录的第N行和第一做对比注意末尾的 null 值！

Lead和Lag函数也可以使用分组，以下是使用 job 分组的例子：

SCOTT@yangdb> select ename,job,sal ,lead(sal,1) over(partition by job order by sal) last_sal from emp;
ENAME      JOB              SAL   LAST_SAL
---------- --------- ---------- ----------
FORD       ANALYST         3000       3000
SCOTT      ANALYST         3000
SMITH      CLERK            800        950
JAMES      CLERK            950       1100
ADAMS      CLERK           1100       1300
MILLER     CLERK           1300
CLARK      MANAGER         2450       2850
BLAKE      MANAGER         2850       2975
JONES      MANAGER         2975
KING       PRESIDENT       5000
MARTIN     SALESMAN        1250       1250
WARD       SALESMAN        1250       1500
TURNER     SALESMAN        1500       1600
ALLEN      SALESMAN        1600
14 rows selected.
SCOTT@yangdb> select ename,job,sal ,lag(sal,1) over(partition by job order by sal) last_sal from emp;
ENAME      JOB              SAL   LAST_SAL
---------- --------- ---------- ----------
FORD       ANALYST         3000
SCOTT      ANALYST         3000       3000
SMITH      CLERK            800
JAMES      CLERK            950        800
ADAMS      CLERK           1100        950
MILLER     CLERK           1300       1100
CLARK      MANAGER         2450
BLAKE      MANAGER         2850       2450
JONES      MANAGER         2975       2850
KING       PRESIDENT       5000
MARTIN     SALESMAN        1250
WARD       SALESMAN        1250       1250
TURNER     SALESMAN        1500       1250
ALLEN      SALESMAN        1600       1500
14 rows selected.
SCOTT@yangdb>

使用分析函数的时候注意空值或者null 给数据带来的影响，数据是否允许为空或者null 计算的时候会导致一定的差错比如 800-null 肯定为null！这个结果是否是应用想要的结果？

细心很重要！！尤其是在计算和钱有关的情况下！！

【Oracle】oracle的LAG和LEAD分析函数

热门文章

最新文章

相关电子书

推荐镜像