select flow_id,rw from (select t.flow_id ,rownum as rw from apex_030200.wwv_flow_list_templates t) where rw >= 5
1.rownum只能用<如果使用>加别名
2.子查询引用只能在查询出的结果中引用，比如子查询没有查出flow_id,外层不能用，另外外层不能引用内层的t
3.薪水前三名，内层查出薪水 order desc的虚表外层使用rownum<3
4.merge可以实现存在数据就update不存在你就insert
merge into product a
using （select 1717 product_id, ‘002‘ req_no from dual b）
on (a.product_id = b.product.id and a.req_no = b.req.no)
when matched then
update set product name = ‘‘.....................
when not matched then
insert () values ()
5.start with connect by 可以查询出一组树的数据,注意最后connect by的条件（父节点=子节点 向上查询 反之向下查询）
可以order排序，可以加入两棵树（or），也可以加入where条件
select * from emp
where......
start with empnc = 7369 or empnc = 7204(注意不能用and )
connect by prior mgr = empno
order by ...
6 份额（查询某数据占有总数据的百分比）
select t.empno,t.ename,t.sal,
100*round(sal/sum(sal) over(),5)
from emp t
7 连续求和(同名分为同组 累加)
select t.empno,t.ename,t.sal,
sum(sal) over(order by sal)
from emp t
8.带条件的连续求和（分部门连续求和）
select t.empno,t.ename,t.sal,t.deptno,
sum(sal) over(partition by t.deptno order by sal)
from emp t
9.分部门总和（取出orderby）
select t.empno,t.ename,t.sal,t.deptno,
sum(sal) over(partition by t.deptno)
from emp t
10工资的分组查询份额（总数的百分比）带上部门分组
select t.empno,t.ename,t.sal,t.deptno,
100*round(sal/sum(sal) over (partition by t.deptno),4)
from emp t
注意这里查询的是“”分组“，因此这里查询的是变成一组为一个100%，查询的是一个部门中员工在本部分所占用的薪水比例
11分组查询出单一条件并分级（查询某一个部门的薪水的级别）注意rank()和row_number()的区别 rank是跳跃性并列(1.1.3.3.5) row_number(1.2.3.4.5)
select t.*,ROW_NUMBER() over(partition by t.deptno order by t.sal desc) rank from emp t
12“总”。。。。。。这个字眼一般使用group by（区分于over（partition by order by））
按部门分组查询部门的总薪水
select sum(t.sal),t.deptno from emp t group by t.deptno
13 总的基础上再次分组 group by + rollup
select sum(t.sal),t.deptno from emp t group by rollup (t.deptno)汇总后将总和进行求和
select sum(t.sal),t.job,t.deptno from emp t group by rollup (t.deptno,t.job)注意多个rollup其实只有第一个参数有效
14cube 连接在order by后面（代替ROLLUP） rollup升级版 全部分组
15grouping实现不用java代码就可以对oracle 查询出的null字段进行赋值 0 本身结果 1合计结果
select sum(t.sal),t.deptno,
(case
when((grouping(t.job)=1 and grouping(t.deptno)=0)) then ‘部门小计‘
when((grouping(t.job)=1 and grouping(t.deptno)=1)) then ‘部门总计‘
else t.job end) as
job from emp t group by rollup (t.deptno,t.job)
16分组后的字段累加(比如按照员工名称，根据月份分组，实现自1月份到12月份工资累加，即二月份是 1月 + 2月 。。)
select t.empno, t.ename, t.sal, sum(sal) over (partition by t.ename order by t.sal desc) from emp t
17分组最高值 最低值 平均值 使用 max() over(partition by order by)代替sum() 还可以用min() avg()
18select * from v$transaction 查看事务
19多层分组函数和子查询之间的冲突问题
select a.CREATOR, a.count_Sum ,b.full_name,b.dept_code,b.area_code from (
select temp.c CREATOR,count(temp.c) as count_Sum from (
select
t.ca,
c.lv,instr(t.ca, ‘,‘, 1, c.lv) + 1,
substr(t.ca,
instr(t.ca, ‘,‘, 1, c.lv) + 1,
instr(t.ca, ‘,‘, 1, c.lv + 1) -
(instr(t.ca, ‘,‘, 1, c.lv) + 1)) AS c
from (select
‘,‘ || checker || ‘,‘ AS ca,
checker,
LENGTH(checker),
length(checker || ‘,‘),
REPLACE(checker, ‘,‘),
length(REPLACE(checker, ‘,‘)),
nvl(length(REPLACE(checker, ‘,‘)), 0),
length(checker || ‘,‘) - nvl(length(REPLACE(checker, ‘,‘)), 0) AS cnt
FROM wm_time_info a where a.check_result !=1) t,
(select LEVEL lv from dual CONNECT BY LEVEL <= 100) c
where c.lv <= t.cnt ) temp group by temp.c) a ,base_user b where a.CREATOR = b.user_code
外层查询和内层分组冲突
--select a.CREATOR, a.count_Sum ,b.full_name,b.dept_code,b.area_code from (
select o.CREATOR,count(o.CREATOR) as count_Sum,FULLNAME,DEPTCODE,AREACODE from (
select temp.c CREATOR,b.full_name FULLNAME,b.dept_code DEPTCODE,b.area_code AREACODE,work_date from
(
select
work_date,
t.ca,
c.lv,
instr(t.ca, ‘,‘, 1, c.lv) + 1,
substr(t.ca,
instr(t.ca, ‘,‘, 1, c.lv) + 1,
instr(t.ca, ‘,‘, 1, c.lv + 1) -
(instr(t.ca, ‘,‘, 1, c.lv) + 1)) AS c
from (
---
select
work_date,
‘,‘ || checker || ‘,‘ AS ca,
checker,
LENGTH(checker),
length(checker || ‘,‘),
REPLACE(checker, ‘,‘),
length(REPLACE(checker, ‘,‘)),
nvl(length(REPLACE(checker, ‘,‘)), 0),
length(checker || ‘,‘) - nvl(length(REPLACE(checker, ‘,‘)), 0) AS cnt
FROM wm_time_info a where a.check_result !=1
---
) t,
(select LEVEL lv from dual CONNECT BY LEVEL <= 100) c
where c.lv <= t.cnt
) temp ,base_user b where temp.c = b.user_code ) o
--where work_date >=‘2016-01-10‘
group by o.CREATOR,FULLNAME,DEPTCODE,AREACODE
--) a ,base_user b where a.CREATOR = b.user_code
20 注意 本条select中的分组和子查询都不可以作为函数的参数传入
原文地址：https://www.cnblogs.com/guohu/p/9082239.html