Pause SQL Execution at Screen Display Time

Question:  I need to have my query “pause” the SQL, stopping execution after the first screen is displayed.  I don’t want to fetch more rows than I need to map out each page, to reduce the overhead and time for the initial screen to display.  How can I stop the fetching of SQL rows after the first screen is displayed? 

Answer:  Oracle provides the first_rows_n (e.g. first_rows_10, first_rows_100) to force the optimizer to optimizer your SQL to start returning rows as quickly as possible, and you can pause SQL after first page map out in PL/SQL.  

The pseudocode might look something like this, where you declare a cursor and fetch the rows, pausing the fetch when you exit the loop to map out the first screen.  Please note that you can also use the PL/SQL BULK COLLECT and FORALL operators for even faster performance:

declare cursor c1 as select /*+ first_rows_100 */ stuff from mytable;

Open cursor c1
Count:=0
LOOP until EOF
      count := count+1
      fetch c1 into :datatruct varray(20)
      If count = 20 then DO
      BEGIN
         Map out the screen
      DONE
END LOOP

Display first page

For more PL/SQL advanced tips, see Dr. Hall’s book, Oracle PL/SQL Tuning.

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