LINQ Any translated differently from v2

Discussed in https://github.com/linq2db/linq2db/discussions/3429

<div type='discussions-op-text'>

^{Originally posted by hkarask February 17, 2022} Hi all,

I’m trying to bump the linq2sql version in an older codebase, from 1.10.2 to 2.0.0 and noticed that LINQ Any gets translated a bit differently:

Given a contrived LINQ statement:

var query =
    from task in con.GetTable<Task>()
    from party in con.GetTable<Party>()
        .Where(p => task.AdminPartyId == p.Id ||
                    con.GetTable<PartyAccess>().Any(pa => pa.PartyId == p.Id && pa.Role == Roles.Admin)
        ).DefaultIfEmpty()
...

I’m seeing different SQL between versions 1 and 2

v 1.10.2

SELECT
 	t.Description,
 	p.Name
 FROM
 	Task t
 		LEFT JOIN Party p ON t.AdminPartyId = p.Id OR EXISTS(
 			SELECT
 				*
 			FROM
 				PartyAccess pa
 			WHERE
 				pa.PartyId = p.Id AND pa.Role = 'Admin'
 		)

v 2.0.0

SELECT
 	j.Description,
 	t2.Name
 FROM
 	Task t
 		LEFT JOIN (
 			SELECT
 				p.Name,
 				p.Id
 			FROM
 				Party p
 			WHERE
 				(EXISTS(
 					SELECT
 						*
 					FROM
 						PartyAccess pa
 					WHERE
 						pa.PartyId = p.Id AND pa.Role = 'Admin'
 				))
 		) t2 ON t.AdminPartyId = t2.Id

There’s now a full sub-query instead of join a level filter. This is causing a full table scan for some reason (using MySql 5.6). Is there a way to revert back to the old behaviour?

Environment details

linq2db version: 1.10.2 & 2.0.0 Database Server: MySql 5.6 Database Provider: MySql.Data 8.0.25 .NET Framework: .NET 4.8

Thanks!

</div>

[MaceWindu]

@sdanyliv planned to look at it. It depends on complexity of required fix - right now we want to concentrate on v4 preparation, so if fix will require a lot of work - it will be postponed till v4, taking into account that there is a workaround…

[hkarask]

Do you think it’s possible to go back to the v1 join behaviour in an upcoming release, at least for MySql?