Lag和Lead函數可以在一次查詢中取出同一字段的前N行的數據和後N行的值。這種操作可以使用對相同表的表連接來實現,不過使用LAG和LEAD有更高的效率。
SCOTT@yangdb> select ename,job,sal ,lag(sal) over(order by sal) last_sal from emp;
ENAME JOB SAL LAST_SAL
---------- --------- ---------- ----------
SMITH CLERK 800 --此時沒有設置default 值 則爲空值
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.
設置了default 值之後 第一行對應的值 爲500
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.
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.
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.
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.
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和Lag函數也可以使用分組,以下是使用 job 分組的例子:
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>