update語句改寫成merge into有時會提高運行速度

看兩個案例

1.根據業務將兩個嵌套子查詢改寫成max，速度有3min提升到3s

UPDATE OPER_792.LL_SCB_YDKB_20120730 A
SET A.DCP =
(SELECT B.PROD_OFFER_NAME
FROM OPER_792.YD_TC B
WHERE A.SERV_ID = B.SERV_ID
AND B.TC_TYPE = '合約計劃'
AND ROWNUM = 1),
A.JCTC =
(SELECT B.PROD_OFFER_NAME
FROM OPER_792.YD_TC B
WHERE A.SERV_ID = B.SERV_ID
AND B.TC_TYPE = '基礎套餐'
AND ROWNUM = 1)
WHERE A.DAY_ID = 20150125


merge into OPER_792.LL_SCB_YDKB_20120730 A
using (select c.SERV_ID,
max(case
when c.TC_TYPE = '合約計劃' then
c.PROD_OFFER_NAME
end) col1,
max(case
when c.TC_TYPE = '基礎套餐' then
c.PROD_OFFER_NAME
end) col2
from OPER_792.YD_TC c
group by c.SERV_ID) b
on (A.SERV_ID = B.SERV_ID and a.day_id = 20150125)
when matched then
update set A.DCP = b.col1, A.JCTC = b.col2

?

2.正常的將update 改寫成merge into

update tb_result r set r.vote_count=nvl((

select temp_.vote_count

from(

　　select result_id,

　　count(rv_id) as vote_count

　　from tb_result_vote

　　group by result_id

) temp_

where temp_.result_id=r.result_id),

r.vote_count

);

?

merge into tb_result r

using(

select result_id,

　　count(rv_id) as vote_count

　　from tb_result_vote

　　group by result_id) temp_

on(temp_.result_id=r.result_id)

when matched then

update set r.vote_count=nvl(temp_.vote_count,r.vote_count);

轉載于:https://www.cnblogs.com/SUN-PH/p/4283247.html

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