Question

I have to fetch data from a running-time-defined table and get data based on a running-time-defined column, I’m now using dynamic sql with ref cursor as below. Is there any more efficient ways to improve the performance ?

PROCEDURE check_error(p_table_name IN VARCHAR2
    ,p_keyword  IN VARCHAR2
    ,p_column_name IN VARCHAR2
    ,p_min_num IN NUMBER
    ,p_time_range IN NUMBER
    ,p_file_desc IN VARCHAR2
    )
IS  
   type t_crs is ref cursor;
   v_cur t_crs;

   v_file_name VARCHAR2(100);
   v_date_started DATE;
   v_date_completed DATE;
   v_counter NUMBER := 0;
   v_sql VARCHAR2(500);
   v_num NUMBER :=0;
BEGIN
   v_sql := 'SELECT '||p_column_name||', DATE_STARTED,DATE_COMPLETED FROM '||p_table_name
            || ' WHERE '||p_column_name||' LIKE '''||p_keyword||'%'' AND  DATE_STARTED > :TIME_LIMIT  ORDER BY '||p_column_name;

    OPEN v_cur FOR v_sql USING (sysdate - (p_time_range/1440));
    LOOP
        FETCH v_cur INTO v_file_name,v_date_started,v_date_completed;
        EXIT WHEN v_cur%NOTFOUND; 
        IF v_date_started IS NOT NULL AND v_date_completed IS NULL   
            AND (sysdate - v_date_started)*1440 > p_time_range THEN
                insert_record(co_alert_stuck,v_file_name,p_table_name,0,p_file_desc,p_time_range);               
        END IF;         
    END LOOP;
END;

BTW, will this make it better ?

v_sql := 'SELECT :COLUMN_NAME1, DATE_STARTED,DATE_COMPLETED FROM :TABLE WHERE :COLUMN_NAME2 LIKE :KEYWORD AND  DATE_STARTED > :TIME_LIMIT  ORDER BY :COLUMN_NAME3';

OPEN v_cur FOR v_sql USING p_column_name,p_table_name,p_column_name,p_keyword||'%',(sysdate - (p_time_range/1440)),p_column_name;

Answer 1

First, I’m not sure that I understand what the code is doing. In the code you posted (which you may have cut down to simplify things), the IF statement checks whether v_date_started IS NOT NULL which is redundant since there is a WHERE clause on DATE_STARTED. It checks whether (sysdate - v_date_started)*1440 > p_time_range which is just a redundant repetition of the WHERE clause on the DATE_STARTED column. And it checks whether v_date_completed IS NULL which would be more efficient as an additional WHERE clause in the dynamic SQL statement that you built. It would make sense to do all of your checks in exactly one place and the most efficient place to do them would be in the SQL statement.

Second, how many rows should this query return and where is the time being spent? If the cursor potentially returns many rows (for some definition of many), you’ll get a bit of efficiency from doing a BULK COLLECT from the cursor into a collection and modifying the insert_record procedure to accept and process a collection. If the time is all spent executing the SQL statement and the query itself returns just a handful of rows, PL/SQL bulk operations would probably not make things appreciably more efficient. If the bottleneck is executing the SQL statement, you’d need to hope that an appropriate index existed on whatever table was passed in. If the bottleneck is the insert_record procedure, we’d need to know what that procedure is doing to comment.

Third, if the insert_record procedure is (at least primarily) just inserting the data that you fetched into a different table, it would be more efficient to get rid of all the looping and just generate a dynamic INSERT statement.

Fourth, with respect to your edit, you cannot use bind variables for table names or column names so the syntax you’re proposing is invalid. It won’t be more efficient because it will generate a bunch of syntax errors.