[英]Oracle: Updating a table column using ROWNUM in conjunction with ORDER BY clause
我想用一個正在運行的整數填充一個表列,所以我在考慮使用ROWNUM。 但是,我需要根據其他列的順序填充它,例如ORDER BY column1, column2
。 不幸的是,這是不可能的,因為Oracle不接受以下語句:
UPDATE table_a SET sequence_column = rownum ORDER BY column1, column2;
也不執行以下語句(嘗試使用WITH子句):
WITH tmp AS (SELECT * FROM table_a ORDER BY column1, column2)
UPDATE tmp SET sequence_column = rownum;
那么,如何在不使用PL / SQL中的游標迭代方法的情況下使用SQL語句來做到這一點呢?
這應該工作(為我工作)
update table_a outer
set sequence_column = (
select rnum from (
-- evaluate row_number() for all rows ordered by your columns
-- BEFORE updating those values into table_a
select id, row_number() over (order by column1, column2) rnum
from table_a) inner
-- join on the primary key to be sure you'll only get one value
-- for rnum
where inner.id = outer.id);
或者,您使用MERGE
語句。 這樣的事情。
merge into table_a u
using (
select id, row_number() over (order by column1, column2) rnum
from table_a
) s
on (u.id = s.id)
when matched then update set u.sequence_column = s.rnum
UPDATE table_a
SET sequence_column = (select rn
from (
select rowid,
row_number() over (order by col1, col2)
from table_a
) x
where x.rowid = table_a.rowid)
但這不會很快,正如Damien指出的那樣,每次更改該表中的數據時,都必須重新運行該語句。
首先創建一個序列:
CREATE SEQUENCE SEQ_SLNO
START WITH 1
MAXVALUE 999999999999999999999999999
MINVALUE 1
NOCYCLE
NOCACHE
NOORDER;
之后,使用以下順序更新表:
UPDATE table_name
SET colun_name = SEQ_SLNO.NEXTVAL;
稍作修正,只需添加AS RN即可 :
UPDATE table_a
SET sequence_column = (select rn
from (
select rowid,
row_number() over (order by col1, col2) AS RN
from table_a
) x
where x.rowid = table_a.rowid)
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