Is there a clever way to the do the following? - mysql

Question

Is ther any clear way of doing the following in one SQL (PL) code? :)
What I have in the tables is the following:
CONTACT_TBL (HEADER)
CONTRACT_ID
BEGIN_DATE
END_DATE
TOT_AMOUNT
123
13-MAY-16
12-MAY-34
100
456
13-JAN-14
12-DEC-25
300
789
13-SEP-14
12-OCT-34
700
CONTRACT_ACTIVTY (DETAIL)
CONTRACT_ID
SEQNUM
END_DATE
AMOUNT
COMMENTS
123
1
12-MAY-19
25
25 - Initial Expiration
123
2
12-MAY-24
25
25
123
3
12-MAY-29
25
25
123
4
12-MAY-34
25
25 - End of Contract
What we need is to populate for each row:
BEGIN_DATE
For SEQNUM #1 - BEGIN_DATE is always CONTACT_TBL.BEGIN_DATE (in this case 13-MAY-15, a 3 year span)
For SEQNUM #2 to N - BEGIN_DATE is 1 day more than previous row's END_DATE (in this case 12-MAY-19 + 1 = 13-MAY-19, all 5 year spans)
Mark the row 'Active' if the SYSDATE is between BEGIN_DATE and END_DATE (in this case it's Row #2)
CONTRACT_ID
SEQNUM
BEGIN_DATE
END_DATE
AMOUNT
STATUS
123
1
13-MAY-16
12-MAY-19
25
123
2
13-MAY-19
12-MAY-24
25
Active
123
3
13-MAY-24
12-MAY-29
25
123
4
13-MAY-29
12-MAY-34
25

Answer 1

N.B. This answer assumes the db is Oracle
This can be done by using LAG to find the date from the previous row.
LAG can accept 3 parameters, the first of which is the column whose value you want to find from the previous row, the second is how many rows to go back each time (default is 1), and the third is what to display if there is no previous row found.
In your case, you want to default to the begin_date from the contact_tbl if there is no previous row to the first row in the contract_activity table, so you need to join the two tables as well, like so:
WITH contact_tbl AS (SELECT 123 contract_id, to_date('13/05/2016', 'dd/mm/yyyy') begin_date, to_date('12/05/2034', 'dd/mm/yyyy') end_date, 100 tot_amount FROM dual UNION ALL
SELECT 456 contract_id, to_date('13/05/2016', 'dd/mm/yyyy') begin_date, to_date('12/05/2034', 'dd/mm/yyyy') end_date, 100 tot_amount FROM dual UNION ALL
SELECT 789 contract_id, to_date('13/05/2016', 'dd/mm/yyyy') begin_date, to_date('12/05/2034', 'dd/mm/yyyy') end_date, 100 tot_amount FROM dual),
contract_activity AS (SELECT 123 contract_id, 1 seqnum, to_date('12/05/2019', 'dd/mm/yyyy') end_date, 25 amount, '25 - Initial Expiration' comments FROM dual UNION ALL
SELECT 123 contract_id, 2 seqnum, to_date('12/05/2024', 'dd/mm/yyyy') end_date, 25 amount, '25' comments FROM dual UNION ALL
SELECT 123 contract_id, 3 seqnum, to_date('12/05/2029', 'dd/mm/yyyy') end_date, 25 amount, '25' comments FROM dual UNION ALL
SELECT 123 contract_id, 4 seqnum, to_date('12/05/2034', 'dd/mm/yyyy') end_date, 25 amount, '25 - End of Contract' comments FROM dual),
-- end of creating subqueries to mimic your tables
contract_details AS (SELECT ca.contract_id,
ca.seqnum,
LAG(ca.end_date + 1, 1, c.begin_date) OVER (PARTITION BY ca.contract_id ORDER BY seqnum) begin_date,
ca.end_date,
ca.amount
FROM contact_tbl c
INNER JOIN contract_activity ca ON c.contract_id = ca.contract_id)
SELECT contract_id,
seqnum,
begin_date,
end_date,
amount,
CASE WHEN TRUNC(SYSDATE) BETWEEN begin_date AND end_date THEN 'Active' END status
FROM contract_details;
CONTRACT_ID SEQNUM BEGIN_DATE END_DATE AMOUNT STATUS
----------- ---------- ----------- ----------- ---------- ------
123 1 13/05/2016 12/05/2019 25
123 2 13/05/2019 12/05/2024 25 Active
123 3 13/05/2024 12/05/2029 25
123 4 13/05/2029 12/05/2034 25
Your status column is a simple case expression, but since it refers to the calculated begin_date, rather than repeating the calculation, I did the begin_date calculation in one subquery, and then referenced that in the outer query.
Note how I used TRUNC(sysdate) instead of just sysdate in the case expression for the status - DATEs in Oracle have a time component (which defaults to midnight if you don't specify the time), so if you ran the query any time between 12/05/2024 00:00:01 and 12/05/2024 23:59:59, your query wouldn't return a status of Active for the second row if you used sysdate. You need to explicitly truncate sysdate to midnight in order for the comparison to work.

Answer 2

Hope below snippet serve the purpose.
DECLARE
CURSOR cur_contracts IS
SELECT
*
FROM
CONTACT_TBL
ORDER BY
CONTRACT_ID;
CURSOR cur_contracts_act(contact_id NUMBER) IS
SELECT
*
FROM
CONTRACT_ACTIVTY
ORDER BY
CONTRACT_ID,
SEQNUM;
l_ca_begin_date DATE;
l_ca_status VARCHAR2(10);
l_prev_rec_end_date DATE;
BEGIN
FOR i IN cur_contracts
LOOP
contract_activity_seq := 0;
FOR j IN cur_contracts_act (i.CONTRACT_ID)
LOOP
contract_activity_seq := contract_activity_seq + 1;
IF (contract_activity_seq = 1) THEN
l_ca_begin_date := i.begin_date;
ELSE
l_ca_begin_date := l_prev_rec_end_date + 1;
END IF;
IF SYSDATE BETWEEN l_ca_begin_date AND j.end_date THEN
l_ca_status := 'Active';
ELSE
l_ca_status := NULL;
END IF;
l_prev_rec_end_date := j.end_date;
UPDATE CONTRACT_ACTIVTY
SET BEGIN_DATE = l_ca_begin_date,
status = l_ca_status
WHERE CURRENT OF cur_contracts_act;
END LOOP;
END LOOP;
COMMIT;
EXCEPTION
WHEN OTHERS THEN raise_application_error(
-20001,
'An error was encountered - ' || SQLCODE || ' -ERROR- ' || SQLERRM
);
END;
/