Update between tables - oracle

Question

I have two tables (ORACLE11) :
TABLE1: (ID_T1 is TABLE1 primary key)
| ID_T1 | NAME | DATEBEGIN | DATEEND |
| 10 | test | 01/01/2017 | 01/06/2017 |
| 11 | test | 01/01/2017 | null |
| 12 | test1 | 01/01/2017 | 01/06/2017 |
| 13 | test1 | 01/01/2017 | null |
TABLE2: (ID_T2 is TABLE2 primary key and ID_T1 is TABLE2 foreign key on TABLE1)
| ID_T2 | ID_T1 |
| 1 | 10 |
| 2 | 11 |
| 3 | 11 |
| 4 | 12 |
| 5 | 13 |
I need to delete all rows from TABLE1 where TABLE1.DATEEND = 'null'
But first I must update TABLE2 to modify TABLE2.ID_T1 to the remaining record in TABLE1 for the same NAME :
TABLE2:
| ID_T2 | ID_T1 |
| 1 | 10 |
| 2 | 10 |
| 3 | 10 |
| 4 | 12 |
| 5 | 12 |
I tried this:
UPDATE TABLE2
SET TABLE2.ID_T1 = (
SELECT TABLE1.ID_T1
FROM TABLE1
WHERE TABLE1.DATEBEGIN = '01/01/2017'
AND TABLE1.DATEEND IS NOT NULL
)
WHERE TABLE2.ID_T1 = (
SELECT TABLE1.ID_T1
FROM TABLE1
WHERE TABLE1.DATEBEGIN = '01/01/2017'
AND TABLE1.DATEEND IS NULL
);
But I don't know how to join on TABLE1.NAME and do it for all rows of TABLE2. Thanks in advance for your help.

Answer 1

First create a temp table to find out which id is to be retained for which name. In the case od multiple possible values, I have selected one by ascending order or id_t1.
create table table_2_update as
select id_t1, name from (select id_t1, name row_number() over(partition by
name order by id_t1) from table1 where name is not null) where rn=1;
Create next table to know which id of table2 connects to which name of table1.
create table which_to_what as
select t2.id_t2, t2.id_t1, t1.name from table1 t1 inner join table2 t2 on
t1.id_t1 = t2.id_t2 group by t2.id_t2, t2.id_t1, t1.name;
Since this newly created table now contains id and name of table1, and id of table2, merge into it to retain one to one case of id and name of table1.
merge into which_to_what a
using table_2_update b
on (a.name=b.name)
when matched then update set
a.id_t1=b.id_t1;
Now finally we have a table which contains the final correct values, you can either rename this tale to table2 or merge original table2 on the basis of id of new table and original table2.
merge into table2 a
using which_to_what a
on (a.id_t2=b.id_t2)
when matched then update set
a.id_t1=b.id_t1;
Finally delete null values from table1.
delete from table1 where dateend is null;

Answer 2

You can do this by joining table1 to itself, joining on the name column. Use the first table (a) to link to table2.id_t1 and the second table (b) to get the t1_id where dateend is not null.
UPDATE table2
SET table2.id_t1 = (
select b.id_t1
from table1 a, table1 b
where a.name = b.name
and b.dateend is not null
and a.id_t1 = table2.id_t1
)
WHERE EXISTS (
select b.id_t1
from table1 a, table1 b
where a.name = b.name
and b.dateend is not null
and a.id_t1 = table2.id_t1
);
This assumes that there will only be one table1 record where dateend is not null.