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How do I speed up a union query in Oracle database?

Posted on 2009-05-04
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Last Modified: 2012-05-06
This is the query:

SELECT EXCEPTION_TYPE, 
NVL(LAST_CHG_DATE, TRUNC(SYSDATE)) LAST_CHG_DATE, HOUSE, CUST,
(CASE WHEN OPER = 'D80' THEN '000' ELSE OPER END) OPER,
(CASE WHEN OPER_NAME = 'USER-ITCDEMO' THEN 'UNKNOWN' ELSE OPER_NAME END) OPER_NAME
FROM
 
 
 
(SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME from EXCEPT_HSI_PHONE_ONLY_CHG
UNION
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_MULT_VID_PKG
UNION
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_MULT_VID_SERV
UNION
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_MULT_VID_BUS
UNION 
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_NO_DVR_CHG
UNION
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_DIG_ST_CHG
UNION
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_SEASONAL
UNION
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_TENANT_CHG
UNION 
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_XF_MISSING
UNION
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_XG_MISSING
UNION 
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_NO_SUBWISE
UNION
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_NO_SALES_REP
UNION
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_CANCEL_NP
UNION 
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_PREF_NEW_VIDEO_ONLY
UNION
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_PREF_NO_3BRONZE
UNION
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_BUS_LITE
 
)
 
WHERE HOUSE <> '118247'

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Question by:libby49
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5 Comments
 
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Accepted Solution

by:
sdstuber earned 125 total points
ID: 24456719
is HOUSE a numeric column?  If so,  

change

WHERE HOUSE <> '118247'
to

WHERE HOUSE <> 118247

what is the distribution of data in each table for various HOUSE values?  Is NOT 118247 a small portion or are you selecting nearly every row in every table.
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LVL 142

Assisted Solution

by:Guy Hengel [angelIII / a3]
Guy Hengel [angelIII / a3] earned 125 total points
ID: 24636945
to really optimize this query, put the condition inside the subquery, and also use UNION ALL instead of UNION

the tip of sdstuber still applies.
SELECT EXCEPTION_TYPE, 
NVL(LAST_CHG_DATE, TRUNC(SYSDATE)) LAST_CHG_DATE, HOUSE, CUST,
(CASE WHEN OPER = 'D80' THEN '000' ELSE OPER END) OPER,
(CASE WHEN OPER_NAME = 'USER-ITCDEMO' THEN 'UNKNOWN' ELSE OPER_NAME END) OPER_NAME
FROM
(SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME from EXCEPT_HSI_PHONE_ONLY_CHG
WHERE HOUSE <> '118247'
UNION ALL
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_MULT_VID_PKG
WHERE HOUSE <> '118247'
UNION ALL
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_MULT_VID_SERV
WHERE HOUSE <> '118247'
UNION ALL
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_MULT_VID_BUS
UNION ALL
WHERE HOUSE <> '118247'
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_NO_DVR_CHG
WHERE HOUSE <> '118247'
UNION ALL
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_DIG_ST_CHG
WHERE HOUSE <> '118247'
UNION ALL
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_SEASONAL
WHERE HOUSE <> '118247'
UNION ALL
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_TENANT_CHG
WHERE HOUSE <> '118247'
UNION ALL
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_XF_MISSING
WHERE HOUSE <> '118247'
UNION ALL
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_XG_MISSING
WHERE HOUSE <> '118247'
UNION ALL
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_NO_SUBWISE
WHERE HOUSE <> '118247'
UNION ALL
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_NO_SALES_REP
WHERE HOUSE <> '118247'
UNION ALL
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_CANCEL_NP
WHERE HOUSE <> '118247'
UNION ALL
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_PREF_NEW_VIDEO_ONLY
WHERE HOUSE <> '118247'
UNION ALL
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_PREF_NO_3BRONZE
WHERE HOUSE <> '118247'
UNION ALL
SELECT EXCEPTION_TYPE, LAST_CHG_DATE, HOUSE, CUST, OPER, OPER_NAME FROM EXCEPT_BUS_LITE
WHERE HOUSE <> '118247'
)

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Expert Comment

by:sdstuber
ID: 24637123
using "UNION ALL" will include duplicates  "UNION" will remove them.

It's not just a performance issue but functionally different.  If your data is already unique between tables then definitely use UNION ALL

if it is not and you want the duplicates then use UNION ALL.

Depending on your database you shouldn't have to put the where clause inside the sub-query.  Oracle, for instance, will push that clause for you
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LVL 142

Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 24637182
>using "UNION ALL" will include duplicates  "UNION" will remove them.
agreed. however, most people starting with sql only know UNION, and never heard about "UNION ALL" in their lessons (blaming the teachers, it was the same for me!)

>Depending on your database you shouldn't have to put the where clause inside the sub-query.  Oracle, for instance, will push that clause for you
from what I know, better safe then sorry... especially as I do migration of sql from one platform to another all the time ...

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