Deal with column list of multiple queries executed at runtime. - plsql

Question

I have a list of queries stored in an Oracle DB table. My requirement is to fetch each of those queries one by one and fire them in a procedure and log their start end and elapsed times in another table
My problem is how should I handle the column list as that's going to be different for each of those queries and the number of columns and their datatypes cannot be anticipated at runtime.
Please suggest a way out.
For now, I have written down the code below. Here I have enclosed each query fetched with a count() to avoid the problem. However, the actual time taken for the count() query will be different from the time taken for the original query to execute.
Thanks a lot!
DECLARE
before_time TIMESTAMP;
after_time TIMESTAMP;
elapsed_time_in_ms NUMBER;
stmnt CLOB; --varchar(32000);
counts NUMBER;
sql_no NUMBER;
err_mess VARCHAR2(100);
CURSOR get_queries
IS
SELECT * FROM SLOW_RUNNING_SQL WHERE curr_ind = 1;
FUNCTION get_elapsed_time(
start_time_in TIMESTAMP ,
end_time_in TIMESTAMP )
RETURN NUMBER
AS
l_days NUMBER;
hours NUMBER;
minutes NUMBER;
seconds NUMBER;
milliseconds NUMBER;
BEGIN
<calculates elapsed time in milliseconds and returns that>
RETURN milliseconds ;
END;
BEGIN
dbms_output.put_line(CURRENT_TIMESTAMP);
before_time := SYSTIMESTAMP;
FOR i IN get_queries
LOOP
stmnt := i.SQL_DESC;
sql_no := i.sql_no;
stmnt := 'SELECT count(*) FROM ('||stmnt||') a';
dbms_output.put_line(stmnt);
EXECUTE IMMEDIATE stmnt INTO counts;
after_time := SYSTIMESTAMP;
elapsed_time_in_ms:= get_elapsed_time(before_time,after_time);
dbms_output.put_line(elapsed_time_in_ms);
INSERT
INTO query_performance_log VALUES
(
i.sql_no,
stmnt,
counts,
before_time,
after_time,
elapsed_time_in_ms/1000,
'No exception',
elapsed_time_in_ms );
dbms_output.put_line(stmnt);
dbms_output.put_line(counts);
dbms_output.put_line(after_time);
dbms_output.put_line(TO_CHAR(after_time - before_time));
COMMIT;
END LOOP;
ROLLBACK;
EXCEPTION
WHEN OTHERS THEN
err_mess:= SQLERRM;
INSERT
INTO query_performance_log VALUES
(
sql_no,
stmnt,
0,
NULL,
NULL,
0,
err_mess,
0
);
dbms_output.put_line(SQLERRM);
ROLLBACK;
END;

Answer 1

A solution that might suit you is to select a constant for every line returned by your query and make a bulk collect INTO a collection of varchar2 variables.
Here is what you're looking for:
-- declare a list of varchar2:
CREATE OR REPLACE TYPE t_my_list AS TABLE OF VARCHAR2(100);
-- then use this type in your proc.:
[..]
declare
v_res t_my_list;
[..]
-- then run the query
execute immediate 'SELECT ''x'' FROM ('||stmnt||') '
bulk collect into v_res;
If the columns selected by your queries are "simple", the above should work fair enough to evaluate performances. But if you start calling other functions and procedures for the data you retrieve in the select, then its more complicate.
In this other case, then you should try to work something out to build a concatenation of the columns returned (and enlarge the VARCHAR2(100) in the declaration of t_my_list). This implies you start work on stmnt and extract the columns, a part being the replacement of , by ''||'' or so.