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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
 
LVL 73

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.
0
 
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
0
 
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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