Consecutively update values starting from a number in the table SQL - sql

Question

I have a question regarding the usage of UPDATE statement. Is there a way for me to code the following scenario with only SQL instead of writing a stored procedure?
I tried to simplify the case.
myTable has 4 columns and its values are as follows:
COMP1 COMP2 NO ACTIVE
0 0 4 N
4 1 Y
2 2 21 Y
3 1 1 Y
1 3 43 Y
2 1 Y
3 1 12 Y
2 2 0 Y
3 2 Y
1 1 5 N
I want to select the values WHERE ACTIVE = 'Y' and start updating
their values in NO column by ordering them by COMP1, COMP2 ASC.
The numbering has to start from the MAX(NO) value in the table WHERE ACTIVE = 'N'
The rows that have same COMP1 and COMP2 will have same NO values.
(Update after comment) NO column is not always NULL. There are erroneous values in this column which are need to be corrected by the update query.
So that, after the UPDATE statement is executed, myTable will be as follows (if we order it)
COMP1 COMP2 NO ACTIVE
0 0 4 N
1 1 5 N
1 3 6 Y
2 1 7 Y
2 2 8 Y
2 2 8 Y
3 1 9 Y
3 1 9 Y
3 2 10 Y
4 1 11 Y
I'm wondering if I would be able to do it without the need to select the whole list and looping in a CURSOR in a stored procedure.
(Update: I've written the SP. A simplified version is as follows. It may have problems since I changed all the names and deleted many conditions.)
PROCEDURE updateAllNo
IS
CURSOR c1
IS
SELECT *
FROM MyTable SE
WHERE SE.ACTIVE = 'Y'
ORDER BY SE.COMP1, SE.COMP2;
v_last_no NUMBER := 0;
v_last_comp2 DATE := SYSDATE + 100;
v_last_comp1 DATE := SYSDATE + 100;
v_now_comp2 DATE := SYSDATE;
v_now_comp1 DATE := SYSDATE;
BEGIN
SELECT MAX (SE.NO)
INTO v_last_no
FROM MyTable SE
WHERE SE.ACTIVE = 'N';
SELECT MAX (SE.COMP1), MAX (SE.COMP2)
INTO v_last_comp1, v_last_comp2
FROM MyTable SE
WHERE SE.ISLEMBASARILI = 'E'
AND SE.NO = v_last_no;
FOR r1 IN c1
LOOP
BEGIN
v_now_comp2 := r1.COMP2;
v_now_comp1 := r1.COMP1;
IF v_now_comp2 != v_last_comp2 OR v_now_comp1 != v_last_comp1
THEN
v_last_no := v_last_no + 1;
END IF;
UPDATE MyTable SE
SET SE.NO = v_last_no
WHERE SEQ_ID = r1.seq_id;
v_last_comp2 := v_now_comp2;
v_last_comp1 := v_now_comp1;
END;
END LOOP;
COMMIT;
END;
I'm using Oracle 11g.

Answer 1

The new number can be retrieved using a window function:
The following will retrieve the active rows and calculate the new value for no
select comp1,
comp2,
row_number() over (order by comp1, comp2) + (select max(no) from mytable where active = 'N') as rn
from mytable
where active = 'Y'
This can now be used in a MERGE statement to run an update against the table. As the table apparently has no PK, I will use the ROWID to match the rows:
merge into mytable tg
using (
select rowid as rid,
comp1,
comp2,
row_number() over (order by comp1, comp2) + (select max(no) from mytable where active = 'N') as rn
from mytable
where active = 'Y'
) t on (t.rid = tg.rowid)
when matched then update
set no = t.rn;
This will most definitely be faster than a loop with single row updates - especially for larger tables.

Answer 2

I am assuming that the field NO is always null when ACTIVE='Y'. If this is the case, then MAX(NO) will return the same value whether or not the WHERE ACTIVE = 'N' condition is specified. With this assumption, this UPDATE statement should do the trick.
UPDATE myTable
SET NO = (SELECT MAX(NO) FROM myTable) + 1
WHERE ROWID IN
(SELECT ROWID FROM myTable
WHERE ACTIVE = 'Y'
ORDER BY COMP1, COMP2);