Help needed in PL/SQL for updating the column for multiple records

Question

Hi,
I am new to PL/SQL and need some help. What is the most effiecient way to update some field in a table as I may need to update thousands of records. I have a coulmn groupid can have multiple records tied to it. All the records attached to some groupid have a priority field also.
How can I update the prorityfield value for all the groupids in a profiecient way. Here is a sample data
GroupId     Priority
1            1
1            2
1            3
1            4
1            5
2            1
2            2
2            3
3            1Here I have three groups 1, 2, 3. Now if any group contains only one record the priority remains same e.g. groupid=3 on top. If any group contains more than one record e.g. groupid=1 & 2 I want to re-arrange the priority fields e.g. If I want to update groupid=1 now if I change the priority of 2 to 5 (make it the last) I want to rearrange the remaing records priority i.e. if 2 becomes 5 as I have 5 rows for groupid=1 then 5 becomes 4, 4 becomes 3, 3 becomes 2 and 1 remains the same.
Same wya if I want to make the priority 1 to 3 for groupid=2 then need 2 to become 1 and 3 to become 2 etc....
Any help is appreciated.
Thanks

Answer 1

Hi,
You don't need PL/SQL to do this (though you can put the following in PL/SQL if you want to):
UPDATE     table_x
SET     priority = CASE
               WHEN  groupid     = 1
               AND   priority = 2
                    THEN  5
               WHEN  groupod     = 1
               AND   priority     BETWEEN 3 AND 5
                    THEN  priority - 1
               WHEN  groupid = 2
               THEN
                    CASE
                         WHEN  prioity = 1
                         THEN  3
                         ELSE  priority - 1
                    END
             END
WHERE     groupId          IN (1, 2)
AND     (     priority     BETWEEN 2 AND 5
     OR     groupid          = 2
     );There are lots of different techniques that can reduce your coidng: for example, the nested CASE statement used for groupid=2 above.
You could do several smaller UPDATEs (for example, one just for groupid=1). Execution will be slower, but coding and testing will be faster.
You could make the "magic numbers" 2 (for groupid=1) and 1 (for groupid=2) variables, even outside of PL/SQL.
If you need more help, post the information that Satyaki requested.