Oracle update based on rownum

Question

I need to write oracle sql to update column with value from unrelated table using rownum.

I cannot get it work:

UPDATE table_1 A
SET A.id = (SELECT B.id FROM table_2 B
         WHERE A.rownum = B.rownum)

Thanks.

Just need to insert value from column ID to another table. There is no columns which are I can use for join but rownum. Is this is possible?

Answer 1

Use MERGE statement instead of UPDATE.
Please find a simple example below.

---

Test data first ( id column in table_2 is null):

create table table_2 as
SELECT LEVEL as id, chr(64+level) as name
from dual connect by level <= 5;

create table table_1 as select * from table_2;
update table_2 set id = null;
commit;

SELECT * FROM table_1;
        ID NAME
---------- ----
         1 A   
         2 B   
         3 C   
         4 D   
         5 E 



SELECT * FROM table_2;
        ID NAME
---------- ----
           A   
           B   
           C   
           D   
           E 

---

This is MERGE command that copier id values from one table to second one basing on their rownumns:

MERGE INTO table_2 t2
USING (
        SELECT *
        FROM (
                select t.*, rownum as rn
                from table_1 t
        ) t1
        JOIN (
                select rownum as rn, rowid as rid
                from table_2 t
        ) t2
        ON t1.rn = t2.rn
) d
ON ( t2.rowid = d.rid )
WHEN MATCHED THEN UPDATE SET t2.id = d.id;

---

And a result after merge is:

SELECT * FROM table_2;
        ID NAME
---------- ----
         1 A   
         2 B   
         3 C   
         4 D   
         5 E