Unclear on LAST_VALUE - Preceding - sql

Question

I have a table that looks like this,
Date Value
01/01/2010 03:59:00 324.44
01/02/2010 09:31:00 NULL
01/02/2010 09:32:00 NULL
.
.
.
01/02/2010 11:42:00 NULL
I want the first valid value to appear in all following rows. This is what I did,
select date,
nvl(value, LAST_VALUE(value IGNORE NULLS) over (order by value RANGE BETWEEN 1 PRECEDING AND CURRENT ROW)) value
from
table
This shows no difference at all, but if I say RANGE BETWEEN 3 PRECEDING AND CURRENT ROW it copies the data to all the rows. I'm not clear why this is happening. Can anyone explain if I'm misunderstanding how to use preceding?

Answer 1

Analytic functions still work on sets of data. They do not process one row at a time, you would need PL/SQL or MODEL to do that. PRECEDING refers to the last X rows, but before the analytic function has been applied.
These problems can be confusing in SQL because you have to build the logic into defining the set, instead of trying to pass data from one row to another. That's why I used CASE with LAST_VALUE in my previous answer.
Edit:
I've added a simple data set so we can all run the exact same query. VALUE1 seems to work to me, am I missing something? Part of the problem with VALUE2 is that the analytic ORDER BY uses VALUE, instead of the date.
select id, the_date, value
,last_value(value ignore nulls) over
(partition by id order by the_date) value1
,nvl(value, LAST_VALUE(value IGNORE NULLS) over
(order by value RANGE BETWEEN 1 PRECEDING AND CURRENT ROW)) value2
from
(
select 1 id, date '2011-01-01' the_date, 100 value from dual union all
select 1 id, date '2011-01-02' the_date, null value from dual union all
select 1 id, date '2011-01-03' the_date, null value from dual union all
select 1 id, date '2011-01-04' the_date, null value from dual union all
select 1 id, date '2011-01-05' the_date, 200 value from dual
)
order by the_date;
Results:
ID THE_DATE VALUE VALUE1 VALUE2
1 1/1/2011 100 100 100
1 1/2/2011 100
1 1/3/2011 100
1 1/4/2011 100
1 1/5/2011 200 200 200

Answer 2

It is possible to copy one row at time because i had done that using java Logic and Sql query
Statement sta;
ResultSet rs,rslast;
try{
//Connection creation code and "con" is an object of Connection Class so don't confuse about that.
sta = con.createStatement();
rs=sta.executeQuery("SELECT * FROM TABLE NAME");
rslast=sta.executeQuery("SELECT * FROM TABLENAME WHERE ID = (SELECT MAX(ID) FROM TABLENAME)");
rslast.next();
String digit =rslast.getString("ID");
System.out.print("ID"+rslast.getString("ID")); // it gives ID of the Last Record.
Instead using this method u can also use ORDER by Date in Descending order.
Now i hope u make logic that only insert Last record.