About a question using Update ... inner join ?

Question

select *
FROM a
INNER JOIN b ON a.ProductID=b.ProductID
WHERE a.HeadID='000246'
this statement is ok ;
But the following statement does not work ! Why ?
UPDATE a SET
a.Quantity=a.PurchaseQuantity/b.ConversionGene
FROM a
INNER JOIN b ON a.ProductID=b.ProductID
WHERE a.HeadID='000246'

Answer 1

"Because Oracle syntactically does not support that type of construct..." Is a correct statement, but not because "It expects only one table in UPDATE statement". The synatax for an updateable join in Oracle requires a "proper" in-line view to be updated.
As long as the table joined (in my example t1) has a declared unique constraint on the columns used to join by (in my example id), you can do it like:
SQL> SELECT * FROM t;
        ID DESCR
         1 One
         2 Two
         3 Three
SQL> SELECT * FROM t1;
        ID DESCR2
         1 Un
         2 Deux
SQL> UPDATE (SELECT t.descr, t1.descr2
  2          FROM t
  3             JOIN t1 ON t.id = t1.id)
  4  SET descr = descr2;
2 rows updated.
SQL> SELECT * FROM t;
        ID DESCR
         1 Un
         2 Deux
         3 ThreeTTFN
John