UPDATE with JOIN syntax for Oracle Database - oracle

Question

First, I execute the following SQL statements.
drop table names;
drop table ages;
create table names (id number, name varchar2(20));
insert into names values (1, 'Harry');
insert into names values (2, 'Sally');
insert into names values (3, 'Barry');
create table ages (id number, age number);
insert into ages values (1, 25);
insert into ages values (2, 30);
insert into ages values (3, 35);
select * from names;
select * from ages;
As a result, the following tables are created.
ID NAME
---------- ----------
1 Harry
2 Sally
3 Barry
ID AGE
---------- ----------
1 25
2 30
3 35
Now, I want to update increment the age of Sally by 1, i.e. set it to 31. The following query works fine.
update ages set age = age + 1 where id = (select id from names where name = 'Sally');
select * from ages;
The table now looks like this.
ID AGE
---------- ----------
1 25
2 31
3 35
I want to know if there is a way it can be done by joins. For example, I tried the following queries but they fail.
SQL> update ages set age = age + 1 from ages, names where ages.id = names.id and names.name = 'Sally';
update ages set age = age + 1 from ages, names where ages.id = names.id and names.name = 'Sally'
*
ERROR at line 1:
ORA-00933: SQL command not properly ended
SQL> update ages set age = age + 1 from names join ages on ages.id = names.id where names.name = 'Sally';
update ages set age = age + 1 from names join ages on ages.id = names.id where names.name = 'Sally'
*
ERROR at line 1:
ORA-00933: SQL command not properly ended

Answer 1

The syntax of the UPDATE statement is:
http://docs.oracle.com/cd/B19306_01/server.102/b14200/statements_10007.htm
where dml_table_expression_clause is:
Please pay attention on ( subquery ) part of the above syntax.
The subquery is a feature that allows to perform an update of joins.
In the most simplest form it can be:
UPDATE (
subquery-with-a-join
)
SET cola=colb
Before update a join, you must know restrictions listed here:
https://docs.oracle.com/cd/B28359_01/server.111/b28286/statements_8004.htm
The view must not contain any of the following constructs:
A set operator
A DISTINCT operator
An aggregate or analytic function
A GROUP BY, ORDER BY, MODEL, CONNECT BY, or START WITH clause
A collection expression in a SELECT list
A subquery in a SELECT list
A subquery designated WITH READ ONLY
Joins, with some exceptions, as documented in Oracle Database Administrator's Guide
and also common rules related to updatable views - here (section: Updating a Join View):
http://docs.oracle.com/cd/B19306_01/server.102/b14231/views.htm#sthref3055
All updatable columns of a join view must map to columns of a
key-preserved table. See "Key-Preserved Tables" for a discussion of
key-preserved tables. If the view is defined with the WITH CHECK
OPTION clause, then all join columns and all columns of repeated
tables are not updatable.
We can first create a subquery with a join:
SELECT age
FROM ages a
JOIN names m ON a.id = m.id
WHERE m.name = 'Sally'
This query simply returns the following result:
AGE
----------
30
and now we can try to update our query:
UPDATE (
SELECT age
FROM ages a
JOIN names m ON a.id = m.id
WHERE m.name = 'Sally'
)
SET age = age + 1;
but we get an error:
SQL Error: ORA-01779:cannot modify a column which maps to a non key-preserved table
This error means, that one of the above restriction is not meet (key-preserved table).
However if we add primary keys to our tables:
alter table names add primary key( id );
alter table ages add primary key( id );
then now the update works without any error and a final outcome is:
select * from ages;
ID AGE
---------- ----------
1 25
2 31
3 35