Comments on: Updation of Oracle tables

By: randym

randym — Thu, 07 Oct 2004 11:19:17 +0000

The problem with the temp table idea is that with orginally stated number of records of 5 million, you will be in effect executing 5 million select statements. That could make it slower than a function.

By: randym

randym — Thu, 07 Oct 2004 11:13:10 +0000

The problem with the temp table idea is that you are going to be in effect executing 5 million (as originally stated number of records to update) select statements on that table. That may result in slow speed. The idea of a function would be quicker and you could write a program to build the function based on the temp table.

By: mangeler

mangeler — Thu, 07 Oct 2004 11:04:04 +0000

I like KShorting’s Idea with a temp table to map the values…

By: kshorting

kshorting — Thu, 07 Oct 2004 10:48:05 +0000

You could try using a decode statement as follows.

update t1 set col2 = decode(col2,’a',’1′,’b',2′)

But with 500 values, I know you will hit a maximum limit for the decode function. You will also have to code all
500 possibilities.

You should be able to store the before and after values in a temporary table and update col2 based on the lookup as follows.

update t1 set (col2) = (select temp.col2_new from temp
where col2_old = t1.col2)

By: randym

randym — Thu, 07 Oct 2004 09:32:26 +0000

A function that basically uses a case statement, If statement or maybe even an array would be efficent.

Your statement would look something like this:
Update t1 set col2 = setvalue(col2).

Your function would look something like this:
create or replace function
setvalue (invalue in varchar2) return varchar2 as
begin
case invalue
when ’1′ then
return(‘a’);
when ’2′ then
return(‘b’);
etc…..
else
return(‘?’);
end case;
end;

The greatest amount of time would probably be spent creating the function. Indexing would make a great difference.

By: vikramranabhatt

vikramranabhatt — Thu, 07 Oct 2004 01:19:37 +0000

u can use stored procedure that will greatly improve the performance. u hav to use index to modify the col2 but if u use store procedure then it will help u

By: mangeler

mangeler — Thu, 07 Oct 2004 01:14:04 +0000

use a cursor to loop through your selected records and update them as required.

By: rickprice

rickprice — Thu, 07 Oct 2004 00:42:53 +0000

Why not use a PL/SQL function or CASE statement to convert the values?

You would then be able to run the update once.

Rick