Why is the FK parent table read

Question

0
SQL Server 2012 Enterprise. I have two tables with a FK relationship. The referencing column in the child table is NOT NULL. The FK is trusted. I create a view that joins the two tables with an INNER JOIN on the foreign key column and no filter. When I SELECT
COUNT(*) from the view, it returns the count of rows in the child table (as expected), but looking at actual execution plan, it reads the parent table to do so. I see no reason to read from the parent table. The trusted FK on a NOT NULL column in the
child table means that for every row in the child table there HAS to be a corresponding row in the parent table, so reading the parent table should be unnecessary. If I change the view's join to an OUTER JOIN, the parent table is not read with a SELECT COUNT(*)
from the view. Is this a shortcoming in the optimizer (not really a bug), or am I missing something? Here's an example:
USE tempdb;
GO
IF OBJECT_ID('dbo.vChild') IS NOT NULL DROP VIEW dbo.vChild;
IF OBJECT_ID('dbo.Child') IS NOT NULL DROP TABLE dbo.Child;
IF OBJECT_ID('dbo.Parent') IS NOT NULL DROP TABLE dbo.Parent;
CREATE TABLE dbo.Parent (PKey int NOT NULL PRIMARY KEY,
 SomeCol varchar(10) NOT NULL);
GO
CREATE TABLE dbo.Child (PKey int NOT NULL,
 SeqNum int NOT NULL,
 CONSTRAINT ChildPK PRIMARY KEY (PKey, SeqNum));
ALTER TABLE dbo.Child WITH CHECK ADD CONSTRAINT FK_Parent_Child FOREIGN KEY(PKey)
 REFERENCES dbo.Parent (PKey);
GO
select is_not_trusted, * from sys.foreign_keys
 WHERE [name] = 'FK_Parent_Child';
GO
CREATE VIEW dbo.vChild AS
SELECT C.PKey, C.SeqNum, P.SomeCol
 FROM dbo.Child AS C
 JOIN dbo.Parent AS P
  ON C.PKey = P.PKey
GO
SELECT COUNT(*) FROM dbo.vChild;
Thanks, Vern
Vern Rabe

Answer 1

I got the same plan as you and I am running SP1 and CU4. I've installed CU4 because of another bug
Confusing error message
Here is my plan as a text:
StmtText
  |--Compute Scalar(DEFINE:([Expr1004]=CONVERT_IMPLICIT(int,[Expr1007],0)))
       |--Stream Aggregate(DEFINE:([Expr1007]=Count(*)))
            |--Nested Loops(Inner Join, OUTER REFERENCES:([C].[PKey]))
                 |--Clustered Index Scan(OBJECT:([tempdb].[dbo].[Child].[ChildPK] AS [C]))
                 |--Clustered Index Seek(OBJECT:([tempdb].[dbo].[Parent].[PK__Parent__5E190D18084EC2A6] AS [P]), SEEK:([P].[PKey]=[tempdb].[dbo].[Child].[PKey] as [C].[PKey]) ORDERED FORWARD)
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