INNER JOIN query - mysql

Question

I'm having trouble optimising a simple SQL query but having serious issue with timing. I've written it three times and none of them work. Here is the original one I was hoping to work:
SELECT RSKADDR.*
FROM EDW_BASE.RCI_RISK_ADDRESS RSKADDR
INNER JOIN (
SELECT DISTINCT COVER_RISK_ID
FROM EDW_BASE.RCI_COVER_RISK_MASTER RSKMASTER
INNER JOIN
(SELECT DISTINCT CONTACT_ID, FOLLOW_UP_DATE
FROM EDW_STG.STG_CIM_SVOM03
WHERE OUTSTANDING = 1 AND QUEUE = 'CIM Update for Contact Address') ADDR_WF
ON RSKMASTER.CONTACT_CODE = ADDR_WF.CONTACT_ID
WHERE RSKMASTER.IS_STORNO != 1
AND RSKMASTER.PRODUCT_CODE = 'HOME'
AND ADDR_WF.FOLLOW_UP_DATE >= RSKMASTER.COVER_EFF_START_DATE
AND RSKMASTER.POLICY_STATUS_CODE = 'POLICY'
AND ADDR_WF.FOLLOW_UP_DATE <= RSKMASTER.COVER_EFF_END_DATE
) ACTVRSK
ON ACTVRSK.COVER_RISK_ID = RSKADDR.RISK_ID
The code in the first inner join works fast all the way to the end. That is, the second SELECT query (within the INNER JOIN query of the first and main SELECT query) works fast without a problem. The problem arises when I integrate the second SELECT query inside the INNER JOIN of the main SELECT query (select RSKADDR.*).
Then it seems the execution is never ending!
I tried other ways and same result:
SELECT RSKADDR.*
FROM EDW_BASE.RCI_RISK_ADDRESS RSKADDR
INNER JOIN EDW_BASE.RCI_COVER_RISK_MASTER RSKMASTER
ON RSKMASTER.COVER_RISK_ID = RSKADDR.RISK_ID
AND RSKMASTER.IS_STORNO != 1
AND RSKMASTER.PRODUCT_CODE = 'HOME'
AND RSKMASTER.POLICY_STATUS_CODE = 'POLICY'
INNER JOIN EDW_STG.STG_CIM_SVOM03 ADDR_WF
ON OUTSTANDING = 1 AND QUEUE = 'CIM Update for Contact Address'
AND RSKMASTER.CONTACT_CODE = ADDR_WF.CONTACT_ID
AND ADDR_WF.FOLLOW_UP_DATE >= RSKMASTER.COVER_EFF_START_DATE
AND ADDR_WF.FOLLOW_UP_DATE <= RSKMASTER.COVER_EFF_END_DATE
It's such an easy query and can't get it to work. How can I do this?

Answer 1

DISTINCT is a costly operation and seldom needed. It often indicates a bad database design or a poorly written query. In your query you are even doing this repeatedly; that doesn't look good.
The second query looks much better. As you say you get the same result, DISTINCT in the first query was superfluous obviously.
I see you doing joins, but all you select is data from one table. So why join then? Select from the table you want data from and put your criteria in WHERE where it belongs.
The following query may be faster, because it plainly shows that we are simply checking whether we find matches in the other tables or not. But then, MySQL was known for not performing too well with IN clauses, so that may depend on the Version you are using.
select *
from edw_base.rci_risk_address
where risk_id in
(
select rm.cover_risk_id
from edw_base.rci_cover_risk_master rm
where rm.is_storno <> 1
and rm.product_code = 'HOME'
and rm.policy_status_code = 'POLICY'
and exists
(
select *
from edw_stg.stg_cim_svom03 adr
where adr.contact_id = rm.contact_code
and adr.follow_up_date >= rm.cover_eff_start_date
and adr.follow_up_date <= rm.cover_eff_end_date
and adr.outstanding = 1
and adr.queue = 'CIM Update for Contact Address'
)
);
Anyway, with your second query or with mine, I suppose the following indexes would help:
create index idx1 on rci_cover_risk_master
(
product_code,
policy_status_code,
is_storno,
contact_code,
cover_eff_start_date,
cover_eff_end_date,
cover_risk_id
);
create index idx2 on stg_cim_svom03
(
contact_id,
follow_up_date,
outstanding,
queue
);
create index idx3 on rci_risk_address(risk_id);

Answer 2

From the query, you only need RSKADDR data, so no need for an INNER JOIN. You can do the same with EXISTS keyword. Try the below query
SELECT RSKADDR.*
FROM EDW_BASE.RCI_RISK_ADDRESS RSKADDR
WHERE EXISTS (
SELECT 1
FROM EDW_BASE.RCI_COVER_RISK_MASTER RSKMASTER
WHERE EXISTS
(SELECT 1
FROM EDW_STG.STG_CIM_SVOM03
WHERE OUTSTANDING = 1 AND QUEUE = 'CIM Update for Contact Address') ADDR_WF
AND RSKMASTER.CONTACT_CODE = ADDR_WF.CONTACT_ID
AND RSKMASTER.IS_STORNO != 1
AND RSKMASTER.PRODUCT_CODE = 'HOME'
AND ADDR_WF.FOLLOW_UP_DATE >= RSKMASTER.COVER_EFF_START_DATE
AND RSKMASTER.POLICY_STATUS_CODE = 'POLICY'
AND ADDR_WF.FOLLOW_UP_DATE <= RSKMASTER.COVER_EFF_END_DATE
)
AND RSKMASTER.COVER_RISK_ID = RSKADDR.RISK_ID
)
Note : I have not tested query as no schema available.