Bug in Ms SQL 2012? TVF giving unexpected result in a outer apply

问题

I'm no expert in Ms SQL, but I came across some really strange behavior in Microsoft SQL Server. I am quite sure it's a bug - but wanted to bring it to more experienced eyes before I conclude that it is. (And I'm not sure how I would go about reporting it to Microsoft if it is).

Environment

@@Version =>

Microsoft SQL Server 2012 - 11.0.5343.0 (X64) 
    May  4 2015 19:11:32 
    Copyright (c) Microsoft Corporation
    Express Edition (64-bit) on Windows NT 6.1 <X64> (Build 7601: Service Pack 1)

Step 1: Create the offending function

I'm going to ask you to create two functions - which should both work the same IMHO, but it seems one of them is acting a little funny. First, the offending function:

if OBJECT_ID('test_function_bad') is not null
    drop function test_function_bad;
go
create function test_function_bad (@val int)
returns table
as return
    (select @val as MyBadValue
     where  @val < 3
    );
go

Next, the almost-identical function which works as expected:

if OBJECT_ID('test_function_good') is not null
    drop function test_function_good;
go
create function test_function_good (@val int)
returns table
as return
    (select @val * 1 as MyGoodValue
        where   @val < 3
    );

Step 2: Create the test table

if OBJECT_ID('tempdb..#test') is not null
    drop table #test;
create table #test (id int, val char);
insert  into #test
        (id, val)
values  (1, 'A'),
        (2, 'B'),
        (3, 'C'),
        (4, 'D');

The Bug (maybe) Run the following code:

select  *
from    #test a
outer apply dbo.test_function_bad(a.id);

And it gives the result:

id          val  MyValue
----------- ---- -----------
1           A    1
2           B    2
3           C    3
4           D    4

That's strange... I expected NULLS instead of the "3" and "4" under MyValue. Why is this function returning values >= 3? It should just return 1 and 2, and nothing else. Right? To confirm this, let's run the following:

select  *
from    #test a
outer apply dbo.test_function_good(a.id);

This works... It gives the following:

id          val  MyValue
----------- ---- -----------
1           A    1
2           B    2
3           C    NULL
4           D    NULL

The Question

Here's the question: Is this really a bug? (I'm guessing some of you experts might be familiar with all sorts of bugs in Ms SQL - but I'm not, this is the first bug I'm seeing. I just want to make sure there's no explanation for this behavior).

Follow up question: If this is a bug, then do I report it to Microsoft? Is there any point in reporting it? Do they care?

Disclaimer: I did try searching for this but didn't find anything.

来源：https://stackoverflow.com/questions/35912354/bug-in-ms-sql-2012-tvf-giving-unexpected-result-in-a-outer-apply

标签

sql-server

sql-server-2012