Question

Quick question about cursors (in particular Oracle cursors).

Let’s say I have a table called “my_table” which has two columns, an ID and a name. There are millions of rows, but the name column is always the string ‘test’.

I then run this PL/SQL script:

declare
 cursor cur is
  select t.id, t.name
    from my_table t
   order by 1;
 begin
   for cur_row in cur loop
     if (cur_row.name = 'test') then
        dbms_output.put_line('everything is fine!');
     else
        dbms_output.put_line('error error error!!!!!');
        exit;
     end if;
   end loop;
 end; 
 /

if I, while this is running, run this SQL:

 update my_table 
   set name = 'error'
  where id = <max id>;
commit;

will the cursor in the PL/SQL block pick up that change and print out “error error error” and exit? or will it not pick up the change at all … or will it even allow the update to my_table?

thanks!

Answer 1

A cursor effectively runs a SELECT and then lets you iterate over the result set, which is kept in a snapshot of the DB state. Because your result set has already been fetched, it won’t be affected by the UPDATE statement. (Handling things otherwise would require you to re-run the query every time you advanced your cursor!)

See:

http://www.techonthenet.com/oracle/cursors/declare.php