分析函数
LAG
语法:
LAG(expr,n ,m) over(partition by expr order by expr)
功能:当前记录前面第n行记录expr列的值。
expr是列字段名称。
n是大于等于0的整数。
m可以为字段值,常量,表达式。
说明:
如果当前记录前面第n行expr列没有值,则返回m。
如果不带参数n,m,则查找当前记录前面一行记录expr列的值,没有则默认值为null。
示例:
返回staffs表中的员工2个月前的工资。 --删除staffs表。 DROP TABLE IF EXISTS staffs; --创建staffs表。 CREATE TABLE staffs ( staff_id NUMBER(6) not null, first_name VARCHAR2(20), last_name VARCHAR2(25), email VARCHAR2(25), phone_number VARCHAR2(20), hire_date DATE, employment_id VARCHAR2(10), salary NUMBER(8,2), commission_pct NUMBER(2,2), manager_id NUMBER(6), section_id NUMBER(4), graduated_name VARCHAR2(60) ); --加入数据。 insert into staffs (staff_id, first_name, last_name, email, phone_number, hire_date, employment_id, salary, commission_pct, manager_id, section_id) values (198, 'Donald', 'OConnell', 'DOCONNEL', '650.507.9833', to_date('21-06-1999', 'dd-mm-yyyy'), 'SH_CLERK', 2200.00, null, 124, 50); insert into staffs (staff_id, first_name, last_name, email, phone_number, hire_date, employment_id, salary, commission_pct, manager_id, section_id) values (198, 'Donald', 'OConnell', 'DOCONNEL', '650.507.9833', to_date('21-06-1999', 'dd-mm-yyyy'), 'SH_CLERK', 2400.00, null, 124, 50); insert into staffs (staff_id, first_name, last_name, email, phone_number, hire_date, employment_id, salary, commission_pct, manager_id, section_id) values (198, 'Donald', 'OConnell', 'DOCONNEL', '650.507.9833', to_date('21-06-1999', 'dd-mm-yyyy'), 'SH_CLERK', 2600.00, null, 124, 50); insert into staffs (staff_id, first_name, last_name, email, phone_number, hire_date, employment_id, salary, commission_pct, manager_id, section_id) values (199, 'Douglas', 'Grant', 'DGRANT', '650.507.9844', to_date('13-01-2000', 'dd-mm-yyyy'), 'SH_CLERK', 4000.00, null, 124, 50); insert into staffs (staff_id, first_name, last_name, email, phone_number, hire_date, employment_id, salary, commission_pct, manager_id, section_id) values (199, 'Douglas', 'Grant', 'DGRANT', '650.507.9844', to_date('13-01-2000', 'dd-mm-yyyy'), 'SH_CLERK', 4200.00, null, 124, 50); insert into staffs (staff_id, first_name, last_name, email, phone_number, hire_date, employment_id, salary, commission_pct, manager_id, section_id) values (199, 'Douglas', 'Grant', 'DGRANT', '650.507.9844', to_date('13-01-2000', 'dd-mm-yyyy'), 'SH_CLERK', 4400.00, null, 124, 50); insert into staffs (staff_id, first_name, last_name, email, phone_number, hire_date, employment_id, salary, commission_pct, manager_id, section_id) values (105, 'David', 'Austin', 'DAUSTIN', '590.423.4569', to_date('25-06-1997', 'dd-mm-yyyy'), 'IT_PROG', 4400.00, null, 103, 60); insert into staffs (staff_id, first_name, last_name, email, phone_number, hire_date, employment_id, salary, commission_pct, manager_id, section_id) values (105, 'David', 'Austin', 'DAUSTIN', '590.423.4569', to_date('25-06-1997', 'dd-mm-yyyy'), 'IT_PROG', 4600.00, null, 103, 60); insert into staffs (staff_id, first_name, last_name, email, phone_number, hire_date, employment_id, salary, commission_pct, manager_id, section_id) values (105, 'David', 'Austin', 'DAUSTIN', '590.423.4569', to_date('25-06-1997', 'dd-mm-yyyy'), 'IT_PROG', 4800.00, null, 103, 60); --返回员工两个月前的工资。 select staff_ID, lag(salary, 2,null)over(partition by staff_ID order by staff_ID) from staffs; 105 105 105 4400 198 198 198 2200 199 199 199 4000 9 rows fetched.
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