Query for getting previous date in oracle in specific scenario - sql

Question

I have the below data in a table A which I need to insert into table B along with one computed column.
TABLE A:
Account_No | Balance | As_on_date
1001 |-100 | 1-Jan-2013
1001 |-150 | 2-Jan-2013
1001 | 200 | 3-Jan-2013
1001 |-250 | 4-Jan-2013
1001 |-300 | 5-Jan-2013
1001 |-310 | 6-Jan-2013
Table B:
In table B, there should be no of days to be shown when balance is negative and
the date one which it has gone into negative.
So, for 6-Jan-2013, this table should show below data:
Account_No | Balance | As_on_date | Days_passed | Start_date
1001 | -310 | 6-Jan-2013 | 3 | 4-Jan-2013
Here, no of days should be the days when the balance has gone negative in recent time and
not from the old entry.
I need to write a SQL query to get the no of days passed and the start date from when the
balance has gone negative.
I tried to formulate a query using Lag analytical function, but I am not succeeding.
How should I check the first instance of negative balance by traversing back using LAG function?
Even the first_value function was given a try but not getting how to partition in it based on negative value.
Any help or direction on this will be really helpful.

Answer 1

Here's a way to achive this using analytical functions.
INSERT INTO tableb
WITH tablea_grouped1
AS (SELECT account_no,
balance,
as_on_date,
SUM (CASE WHEN balance >= 0 THEN 1 ELSE 0 END)
OVER (PARTITION BY account_no ORDER BY as_on_date)
grp
FROM tablea),
tablea_grouped2
AS (SELECT account_no,
balance,
as_on_date,
grp,
LAST_VALUE (
balance)
OVER (
PARTITION BY account_no, grp
ORDER BY as_on_date
ROWS BETWEEN UNBOUNDED PRECEDING
AND UNBOUNDED FOLLOWING)
closing_balance
FROM tablea_grouped1
WHERE balance < 0
AND grp != 0 --keep this, if starting negative balance is to be ignored
)
SELECT account_no,
closing_balance,
MAX (as_on_date),
MAX (as_on_date) - MIN (as_on_date) + 1,
MIN (as_on_date)
FROM tablea_grouped2
GROUP BY account_no, grp, closing_balance
ORDER BY account_no, MIN (as_on_date);
First, SUM is used as analytical function to assign group number to consecutive balances less than 0.
LAST_VALUE function is then used to find the last -ve balance in each group
Finally, the result is aggregated based on each group. MAX(date) gives the last date, MIN(date) gives the starting date, and the difference of the two gives number of days.
Demo at sqlfiddle.

Answer 2

Try this and use gone_negative to computing specified column value for insert into another table:
select temp.account_no,
temp.balance,
temp.prev_balance,
temp.on_date,
temp.prev_on_date,
case
WHEN (temp.balance < 0 and temp.prev_balance >= 0) THEN
1
else
0
end as gone_negative
from (select account_no,
balance,
on_date,
lag(balance, 1, 0) OVER(partition by account_no ORDER BY account_no) prev_balance,
lag(on_date, 1) OVER(partition by account_no ORDER BY account_no) prev_on_date
from tblA
order by account_no) temp;
Hope this helps pal.

Answer 3

Here's on way to do it.
Select all records from my_table where the balance is positive.
Do a self-join and get all the records that have a as_on_date is greater than the current row, but the amounts are in negative
Once we get these, we cut-off the rows WHERE the date difference between the current and the previous row for as_on_date is > 1. We then filter the results a outer sub query
The Final select just groups the rows and gets the min, max values for the filtered rows which are grouped.
Query:
SELECT
account_no,
min(case when row_number = 1 then balance end) as balance,
max(mt2_date) as As_on_date,
max(mt2_date) - mt1_date as Days_passed,
min(mt2_date) as Start_date
FROM
(
SELECT
*,
MIN(break_date) OVER( PARTITION BY mt1_date ) AS min_break_date,
ROW_NUMBER() OVER( PARTITION BY mt1_date ORDER BY mt2_date desc ) AS row_number
FROM
(
SELECT
mt1.account_no,
mt2.balance,
mt1.as_on_date as mt1_date,
mt2.as_on_date as mt2_date,
case when mt2.as_on_date - lag(mt2.as_on_date,1) over () > 1 then mt2.as_on_date end as break_date
FROM
my_table mt1
JOIN my_table mt2 ON ( mt2.balance < mt1.balance AND mt2.as_on_date > mt1.as_on_date )
WHERE
MT1.balance > 0
order by
mt1.as_on_date,
mt2.as_on_date ) sub_query
) T
WHERE
min_break_date is null
OR mt2_date < min_break_date
GROUP BY
mt1_date,
account_no
SQLFIDDLE
I have a added a few more rows in the FIDDLE, just to test it out