[英]Keep the last 20 records and delete other records in oracle sql
我想在VMR
表中保留最后20条记录,并删除所有其他记录。 VMR表具有5000000
条记录,并且正在增长。 我也有create_date列,该列在VMR
表中具有date datatype
,并且具有非唯一索引。 我尝试使用rownum删除记录,并使用下面的查询保留最后20条记录,但是删除它花费了太多时间。 还有其他方法可以更快地运行查询。
delete from VMR
where rowid not in
(select rowid
from VMR
where rownum <=20);
只是为了显示一个替代方案:
-- get 20 last records and remember them
create table vmr20 as
select * from vmr order by create_date desc fetch first 20 rows only;
-- empty table via DDL which should be fastest
truncate vmr;
-- re-insert the last 20 rows
insert into vmr
select * from vmr20;
-- delete temp table
drop table vmr20;
尝试使用ROW_NUMBER()
WITH CTE AS (
SELECT t.*,
ROW_NUMBER() OVER(ORDER BY create_date DESC) as rnk
FROM VMR t)
DELETE FROM CTE
WHERE CTE.rnk > 20
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