On Thu, Apr 7, 2016 at 2:27 PM, Gabor Boros gaborboros@... [firebird-support] <firebird-support@yahoogroups.com> wrote:

2016. 04. 07. 19:31 keltezéssel, 'Mark Rotteveel' mark@...
[firebird-support] írta:
>
>
> For a join (inner join), the rows must exist in both tables, so both
> tables need to be evaluated.
>

I understand this. Try describe my problem with other words.
Is the VIEW an atomic (or compiled like a STORED PROCEDURE) thing?

For views, only the view definition is stored.  When a query references a view,

the view is compiled and optimized like any other query.  If possible, it is 

integrated into the larger query. 

 

I have a VIEW with 4 fields (FIELD1..4), 1 come from the "FROM table"
(FIELD1) and 3 from JOINs (FIELD2..4). If execute a SELECT FIELD1 FROM
... PLAN contains the JOINs. Why? If I write a SELECT manually not
include JOINs if not needed for the resulted fields, because want
maximum performance.

As Mark and others explained, both sides of a join must always be 

evaluated, even if you reference only fields from one table.  Consider

this case:

     select d.DepartmentName from Departments d

            join Employees e on e.DeptID = d.DeptID

Suppose there are no Employees at all, but 10 Departments.  That

query should return no results because what was asked was to return

the DepartmentName of Departments with Employees.

Suppose you again have 10 Departments, but only 1 Employee and

that Employee has a DeptID that matches one of the Departments.

Then the query should return one DepartmentName.

Suppose you have 10 Departments and 10 Employees, but all the

Employees have the same DeptID.  Then you should get the same

DepartmentName ten times.

You're thinking of a case where there is a (possibly unstated) referential

relationship between the table that you're getting fields from and the other

table in the view.  The table you're getting data from is the referencing

table and the other is the referenced table.  In that particular case, the

join doesn't matter, but there's no way that Firebird can know that. 

Good luck,

Ann