平移： lag/lead over 函式

1. oralce內建的高階函式，可以獲取到當前查詢結果集中每一行的前幾行，相當於做了垂直方向的平移
2. 要注意的函式作用域是此次查詢結果集，雖然提供了分組的功能，只是對當前結果集的分組
3. lagover
4. sample

with tmp as(
select '1' id ,'aa' name ,'19' age from dual union all
select '31' id ,'aa' name ,'31' age from dual union all
select '2' id ,'bb' name ,'20'
 
 age from dual union all
select '3' id ,'CC' name ,'21' age from dual
)
select a.*,
       lag(age,1) over (order by name, id asc) lag,
      a.age - lag(age,1) over (order by id asc) lag1
from tmp a;

填充： 關聯

1. 通過利用rownum做一次逆序排列，對null值用其之前不為0的數值填充
2. with a as (), b as () select * from a; 快取表資料
3. sample

with test as (
select rownum rn, id, age from(
select '1' id , 19 age from dual union all
select '2' id , null age from dual union all
select '3' id , null age from dual union all
select '4' id , 21 age from dual union all
select '5' id , 0 age from dual  )
),
test2 as (select * from test order
 
 by rn desc)
select tm.id, tm.age, 
  ( select t2.age from test2 t2 
  where t2.rn <= tm.rn and t2.age > 0 and rownum = 1) agepad
      from test tm;