Query Execution Time Varies - IBM Informix - Data Studio - informix

Question

I am executing one SQL statement in Informix Data Studio 12.1. It takes around 50 to 60 ms for execution(One day date).
SELECT
sum( (esrt.service_price) * (esrt.confirmed_qty + esrt.pharmacy_confirm_quantity) ) AS net_amount
FROM
episode_service_rendered_tbl esrt,
patient_details_tbl pdt,
episode_details_tbl edt,
ms_mat_service_header_sp_tbl mmshst
WHERE
esrt.patient_id = pdt.patient_id
AND edt.patient_id = pdt.patient_id
AND esrt.episode_id = edt.episode_id
AND mmshst.material_service_sp_id = esrt.material_service_sp_id
AND mmshst.bill_heads_id = 1
AND esrt.delete_flag = 1
AND esrt.customer_sp_code != '0110000006'
AND pdt.patient_category_id IN(1001,1002,1003,1004,1005,1012,1013)
AND edt.episode_type ='ipd'
AND esrt.generated_date BETWEEN '2017-06-04' AND '2017-06-04';
When i am trying to execute the same by creating function it takes around 35 to 40 Seconds for execution.
Please find the code below.
CREATE FUNCTION sb_pharmacy_account_summary_report_test1(START_DATE DATE,END_DATE DATE)
RETURNING VARCHAR(100),DECIMAL(10,2);
DEFINE v_sale_credit_amt DECIMAL(10,2);
BEGIN
SELECT
sum( (esrt.service_price) * (esrt.confirmed_qty +
esrt.pharmacy_confirm_quantity) ) AS net_amount
INTO
v_sale_credit_amt
FROM
episode_service_rendered_tbl esrt,
patient_details_tbl pdt,
episode_details_tbl edt,
ms_mat_service_header_sp_tbl mmshst
WHERE
esrt.patient_id = pdt.patient_id
AND edt.patient_id = pdt.patient_id
AND esrt.episode_id = edt.episode_id
AND mmshst.material_service_sp_id = esrt.material_service_sp_id
AND mmshst.bill_heads_id = 1
AND esrt.delete_flag = 1
AND esrt.customer_sp_code != '0110000006'
AND pdt.patient_category_id IN(1001,1002,1003,1004,1005,1012,1013)
AND edt.episode_type ='ipd'
AND esrt.generated_date BETWEEN START_DATE AND END_DATE;
RETURN 'SALE CREDIT','' with resume;
RETURN 'IP SB Credit Amount',v_sale_credit_amt;
END
END FUNCTION;
Can someone tell me what is the reason for this time variation?

Answer 1

..in very easy words.
If you create a function the sql is parsed and stored with some optimization stuff in the database. If you call the function, optimizer knows about the sql and execute it. So optimization is done only once, if you create the function.
If you run the SQL, Optimizer parse the sql, optimizes it and then execute it, every time you execute the SQL.
This explains the time difference.

Answer 2

I would say the difference in time is due the parametrized query.
The first SQL has hardcoded dates values, the one in the SPL has parameters. That may cause a different query plan (e.g: which index to follow) to be applied to the query in the SPL than the one executed from Data Studio.
You can try getting the query plan (using set explain) from the first SQL and then use directives in the SPL to force the engine to use that same path.
have a look at:
https://www.ibm.com/support/knowledgecenter/SSGU8G_12.1.0/com.ibm.perf.doc/ids_prf_554.htm
it explains how to use optimizer directives to speed up queries.