[Oracle] UPDATE FROM: implement correlated update support

Hi!

I think Oracle has more good candidate for such thing:

UPDATE
  [UpdatedEntities]
SET
  ( [Value1], [Value2], [Value3] ) = 
  (
    SELECT
      ([UpdatedEntities].[Value1] * [t].[Value1]) * @int1,
      ([UpdatedEntities].[Value2] * [t].[Value2]) * @int2,
      ([UpdatedEntities].[Value3] * [t].[Value3]) * @int3
    FROM
      [NewEntities] [t] 
    WHERE
      [t].[id] <> @someId AND [UpdatedEntities].[id] = [t].[id]
  )
WHERE
  EXISTS(
    SELECT
      *
    FROM
       [NewEntities] [t6] 
    WHERE
      [t6].[id] <> @someId AND [UpdatedEntities].[id] = [t6].[id]
  )

_Originally posted by @AndrePScope in https://github.com/linq2db/linq2db/pull/1278#issuecomment-620851672_

[sdanyliv]

@viceroypenguin. Oracle is the rule-breaker, WITH statements in such case will not work. Oracle sticks WITH statement with SELECT, not whole query.

[jods4]

@sdanyliv tangentially related: is there a syntax to write a “tuple” (not sure what’s the right word) update in Oracle manually?

I.e. can you write this with linq2db?

update X set (a, b) = (1, 2)
-- or with a subselect
update X set (a, b) = (select 1, 2 from dual)