Oracle高效的SQL語句之分析函式彙總
阿新 • • 發佈：2022-05-18
實際應用中我們可以通過sum()統計出組中的總計或者是累加值，具體示例如下：
1.建立演示表
create table emp
as
select * from scott.emp;
alter table emp
add constraint emp_pk
primary key(empno);
create table dept
as
select * from scott.dept;
alter table dept
add constraint dept_pk
primary key(deptno);
2. sum()語句如下：
select deptno,
ename,
sal,
--按照部門薪水累加（order by改變了分析函式的作用，只工作在當前行和前一行，而不是所有行）
sum(sal) over (partition by deptno order by sal) CumDeptTot,
sum(sal) over (partition by deptno) SalByDept, --統計一個部門的薪水
sum(sal) over (order by deptno,sal) CumTot, --所有僱員的薪水一行一行的累加
sum(sal) over () TotSal --統計總薪水
from emp
order by deptno, sal
3. 結果如下：
10 MILLER 1300.00 1300 8750 1300 29025
10 CLARK 2450.00 3750 8750 3750 29025
10 KING 5000.00 8750 8750 8750 29025
20 SMITH 800.00 800 10875 9550 29025
20 ADAMS 1100.00 1900 10875 10650 29025
20 JONES 2975.00 4875 10875 13625 29025
20 SCOTT 3000.00 10875 10875 19625 29025
20 FORD 3000.00 10875 10875 19625 29025
30 JAMES 950.00 950 9400 20575 29025
30 WARD 1250.00 3450 9400 23075 29025
30 MARTIN 1250.00 3450 9400 23075 29025
30 TURNER 1500.00 4950 9400 24575 29025
30 ALLEN 1600.00 6550 9400 26175 29025
30 BLAKE 2850.00 9400 9400 29025 29025
[Oracle]高效的SQL語句之分析函式(二)--max()
如果我們按照示例想得到每個部門薪水值最高的僱員的紀錄，可以有四種方法實現：
先建立示例表
create table emp
as
select * from scott.emp;
alter table emp
add constraint emp_pk
primary key(empno);
create table dept
as
select * from scott.dept;
alter table dept
add constraint dept_pk
primary key(deptno);
方法1.emp中的每一行都會進行max比較，費時
select * from emp emp1 where emp1.sal=(select max(emp2.sal) from emp emp2 where emp2.deptno=emp1.deptno)
方法2.先子查詢查找出max sal，然後與emp表相關聯，如果邏輯複雜會產生較多程式碼
select * from emp emp1,(select deptno,max(sal) maxsal from emp emp2 group by emp2.deptno) emp3 where emp1.deptno=emp3.deptno and emp1.sal=emp3.maxsal
方法3.使用max分析函式
select deptno,maxsal,empno from(
select max(sal) over (partition by deptno) maxsal,emp.* from emp) emp2
where emp2.sal=emp2.maxsal
方法4.使用dense_rank分析函式，如果一個部門可能存在多筆最大薪水，就不能使用row_number()分析函式
select deptno,sal,empno from(
select emp.*,DENSE_RANK() over (partition by deptno order by sal desc) rownumber from emp) emp2
where rownumber=1
結果如下：
10 5000.00 7839
20 3000.00 7788
20 3000.00 7902
30 2850.00 7698
[Oracle]高效的SQL語句之分析函式(三)--row_number() /rank()/dense_rank()
有些時候我們希望得到指定資料中的前n列，示例如下：
得到每個部門薪水最高的三個僱員：
先建立示例表
create table emp
as
select * from scott.emp;
alter table emp
add constraint emp_pk
primary key(empno);
create table dept
as
select * from scott.dept;
alter table dept
add constraint dept_pk
primary key(deptno);
先看一下row_number() /rank()/dense_rank()三個函式之間的區別
select emp.deptno,emp.sal,emp.empno,row_number() over (partition by deptno order by sal desc) row_number, --1,2,3
rank() over (partition by deptno order by sal desc) rank, --1,1,3
dense_rank() over (partition by deptno order by sal desc) dense_rank from emp --1,1,2
結果如下:
10 5000.00 7839 1 1 1
10 2450.00 7782 2 2 2
10 1300.00 7934 3 3 3
20 3000.00 7788 1 1 1
20 3000.00 7902 2 1 1
20 2975.00 7566 3 3 2
20 1100.00 7876 4 4 3
20 800.00 7369 5 5 4
30 2850.00 7698 1 1 1
30 1600.00 7499 2 2 2
取每個部門的薪水前三位僱員：
select t.deptno,t.rank,t.sal from
(
select emp.*,row_number() over (partition by deptno order by sal desc) row_number, --1,2,3
rank() over (partition by deptno order by sal desc) rank, --1,1,3
dense_rank() over (partition by deptno order by sal desc) dense_rank from emp --1,1,2
) t
where t.rank<=3
結果如下：
10 1 5000.00
10 2 2450.00
10 3 1300.00
20 1 3000.00
20 1 3000.00
20 3 2975.00
30 1 2850.00
30 2 1600.00
30 3 1500.00
如果想輸出成deptno sal1 sal2 sal3這種型別的格式
步驟一（decode）：
select t.deptno,decode(row_number,1,sal) sal1,decode(row_number,2,sal) sal2,decode(row_number,3,sal) sal3 from
(
select emp.*,row_number() over (partition by deptno order by sal desc) row_number, --1,2,3
rank() over (partition by deptno order by sal desc) rank, --1,1,3
dense_rank() over (partition by deptno order by sal desc) dense_rank from emp --1,1,2
) t
where t.rank<=3
結果如下：
10 5000
10 2450
10 1300
20 3000
20 3000
20 2975
30 2850
30 1600
30 1500
步驟二（使用聚合函式去除null,得到最終結果）：
select t.deptno,max(decode(row_number,1,sal)) sal1,max(decode(row_number,2,sal)) sal2,max(decode(row_number,3,sal)) sal3 from
(
select emp.*,row_number() over (partition by deptno order by sal desc) row_number, --1,2,3
rank() over (partition by deptno order by sal desc) rank, --1,1,3
dense_rank() over (partition by deptno order by sal desc) dense_rank from emp --1,1,2
) t
where t.rank<=3
group by t.deptno
結果如下：
10 5000 2450 1300
20 3000 3000 2975
30 2850 1600 1500
[Oracle]高效的SQL語句之分析函式(四)--lag()/lead()
有時候報表上面需要顯示該筆操作的上一步驟或者下一步驟的詳細資訊，這個時候可以按照下面的做法：
先建立示例表：
-- Create table
create table LEAD_TABLE
(
CASEID VARCHAR2(10),
STEPID VARCHAR2(10),
ACTIONDATE DATE
)
tablespace COLM_DATA
pctfree 10
initrans 1
maxtrans 255
storage
(
initial 64K
minextents 1
maxextents unlimited
);
insert into LEAD_TABLE values('Case1','Step1',to_date('20070101','yyyy-mm-dd'));
insert into LEAD_TABLE values('Case1','Step2',to_date('20070102','yyyy-mm-dd'));
insert into LEAD_TABLE values('Case1','Step3',to_date('20070103','yyyy-mm-dd'));
insert into LEAD_TABLE values('Case1','Step4',to_date('20070104','yyyy-mm-dd'));
insert into LEAD_TABLE values('Case1','Step5',to_date('20070105','yyyy-mm-dd'));
insert into LEAD_TABLE values('Case1','Step4',to_date('20070106','yyyy-mm-dd'));
insert into LEAD_TABLE values('Case1','Step6',to_date('20070101','yyyy-mm-dd'));
insert into LEAD_TABLE values('Case1','Step1',to_date('20070201','yyyy-mm-dd'));
insert into LEAD_TABLE values('Case2','Step2',to_date('20070202','yyyy-mm-dd'));
insert into LEAD_TABLE values('Case2','Step3',to_date('20070203','yyyy-mm-dd'));
commit;
每一條記錄都能連線到上/下一行的內容
select caseid,stepid,actiondate,lead(stepid) over (partition by caseid order by actiondate) nextstepid,
lead(actiondate) over (partition by caseid order by actiondate) nextactiondate,
lag(stepid) over (partition by caseid order by actiondate) prestepid,
lag(actiondate) over (partition by caseid order by actiondate) preactiondate
from lead_table
結果如下：
Case1 Step1 2007-1-1 Step2 2007-1-2
Case1 Step2 2007-1-2 Step3 2007-1-3 Step1 2007-1-1
Case1 Step3 2007-1-3 Step4 2007-1-4 Step2 2007-1-2
Case1 Step4 2007-1-4 Step5 2007-1-5 Step3 2007-1-3
Case1 Step5 2007-1-5 Step4 2007-1-6 Step4 2007-1-4
Case1 Step4 2007-1-6 Step6 2007-1-7 Step5 2007-1-5
Case1 Step6 2007-1-7 Step4 2007-1-6
Case2 Step1 2007-2-1 Step2 2007-2-2
Case2 Step2 2007-2-2 Step3 2007-2-3 Step1 2007-2-1
Case2 Step3 2007-2-3 Step2 2007-2-2
還可以進一步統計一下兩者的相差天數
select caseid,stepid,actiondate,nextactiondate,nextactiondate-actiondate datebetween from (
select caseid,stepid,actiondate,lead(stepid) over (partition by caseid order by actiondate) nextstepid,
lead(actiondate) over (partition by caseid order by actiondate) nextactiondate,
lag(stepid) over (partition by caseid order by actiondate) prestepid,
lag(actiondate) over (partition by caseid order by actiondate) preactiondate
from lead_table)
結果如下：
Case1 Step1 2007-1-1 2007-1-2 1
Case1 Step2 2007-1-2 2007-1-3 1
Case1 Step3 2007-1-3 2007-1-4 1
Case1 Step4 2007-1-4 2007-1-5 1
Case1 Step5 2007-1-5 2007-1-6 1
Case1 Step4 2007-1-6 2007-1-7 1
Case1 Step6 2007-1-7
Case2 Step1 2007-2-1 2007-2-2 1
Case2 Step2 2007-2-2 2007-2-3 1
Case2 Step3 2007-2-3