Oracle：结合使用 ROWNUM 和 ORDER BY 子句更新表列

Question

我想用连续的整数填充表列，所以我考虑使用 ROWNUM。但是，我需要根据其他列的顺序填充它，例如 ORDER BY column1, column2。不幸的是，这是不可能的，因为 Oracle 不接受以下语句：

UPDATE table_a SET sequence_column = rownum ORDER BY column1, column2;

也不接受以下语句（尝试使用WITH子句）：

WITH tmp AS (SELECT * FROM table_a ORDER BY column1, column2)
UPDATE tmp SET sequence_column = rownum;

那么我如何使用 SQL 语句而不诉诸 PL/SQL 中的游标迭代方法来做到这一点？

Answer 1

这应该有效（对我有效）

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 语句。像这样的东西。

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

Answer 2

 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)

但这不会很快，正如 Damien 指出的那样，每次更改该表中的数据时都必须重新运行此语句。

Answer 3

首先创建一个序列：

CREATE SEQUENCE SEQ_SLNO
  START WITH 1
  MAXVALUE 999999999999999999999999999
  MINVALUE 1
  NOCYCLE
  NOCACHE
  NOORDER;

然后使用序列更新表：

UPDATE table_name
SET colun_name = SEQ_SLNO.NEXTVAL;

Answer 4

一个小修正只需添加 AS RN ：

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)