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04.16.2008 at 07:47AM PDT, ID: 23327302

	[x] Attachment Details

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9.1

Simple Subquery not working

Zone: MS SQL Server

Tags: Microsoft, SQL, 2000

Sorry its either too early in the morning or i have left my brain at home - I just need to be put out of my misery.

I have two tables (which I have simplified but still same idea). One has all the details of the staff with their extension and supervisor name. I have another table which will list the supervisors, their extension and their managers. So at the moment I two tables:

StaffDetails Table.....

StaffName Supervisor Ext
Bob Gary 123
Mary Gary 112
Jane Mark 111
Peter Tony 101
Sandy Tony 101

StaffSupervisors Table.....

Supervisor Ext Manager
Gary 501 Steve
Mark 502 Alan

As you can see in the StaffDetails table, there are staff members Peter and Sandy who have Tony as their supervisor. But the details of Tony havent been put into the StaffSupervisors table - yet.

So as not to duplicate entries into the Supervisor table, I thought of using the coding in the code snippet below.

However - it returns zero results. If i run the select alone it returns zero results. If it change the query to look for "IN" instead of "NOT IN" it returns "Gary" and "Mark" as expected.

Please tell me I am stupid and I am missing the obvious, I have done thousands of queries like this and I am stumped as to why this isnt working at my new job.

         
             insert into staffsupervisors (supervisor)
select distinct supervisor 
  from staffdetails
 where supervisor not in (select supervisor from staffsupervisors)

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Question Stats

Zone: Microsoft

Question Asked By: Wedmore

Solution Provided By: ScottPletcher

Participating Experts: 4

Solution Grade: A

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04.16.2008 at 07:56AM PDT, ID: 21368481

orcic:

Try different aproach:
insert into staffsupervisors (supervisor)
select distinct sd.supervisor
from staffdetails sd
left join staffsupervisors ss on ss.supervisor=sd.supervisor
where ss.supervisor is null

04.16.2008 at 08:05AM PDT, ID: 21368581

Wedmore:

I know that works, I am more concerned as to why the NOT IN wont work. There has to be a reason.

04.16.2008 at 08:07AM PDT, ID: 21368603

Rank: Wizard

ee_rlee:

hi, try if this works

insert into staffsupervisors (supervisor)
select distinct supervisor
from staffdetails
where staffdetails.supervisor not in (select supervisor from staffsupervisors)

04.16.2008 at 08:23AM PDT, ID: 21368783

Wedmore:

Nope - still zero results.

If i run the subquery "select supervisor from staffsupervisors" alone it does pull the list of supervisors in the table.

I even ran an update to remove any spaces which might cause an issue....grrr, i'm not the only one that thinks this is weird right?

update staffdetails
set supervisor = rtrim(ltrim(supervisor))

04.16.2008 at 08:29AM PDT, ID: 21368851

Rank: Wizard

ee_rlee:

Does this return any records?

select distinct supervisor
from staffdetails
where staffdetails.supervisor not in (select supervisor from staffsupervisors)

04.16.2008 at 08:36AM PDT, ID: 21368939

Wedmore:

Nope - nothing.

And again - if i change it from "NOT IN" to "IN", it will return the correct number of records.

04.16.2008 at 08:43AM PDT, ID: 21369015

Wedmore:

Just to recap....

This works:
select distinct sd.supervisor
from staffdetails sd
left join staffsupervisors ss on ss.supervisor=sd.supervisor
where ss.supervisor is null

This doesnt work:
select distinct supervisor
from staffdetails
where staffdetails.supervisor not in (select supervisor from staffsupervisors)

I know I know I know. I could use the first query, but I have a habit of using subqueries from time to time, so if something so simple isnt working, I'd like to know now rather than a large join with multiple tables etc.

04.16.2008 at 09:45AM PDT, ID: 21369714

orcic:

what about
select distinct supervisor
from staffdetails
where ltrim(rtrim(supervisor)) not in (select ltrim(rtrim(supervisor)) from staffsupervisors)

04.16.2008 at 09:49AM PDT, ID: 21369748

Rank: Wizard

ee_rlee:

I tried the query and it is returning Tony.

                       
         
           
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             create table StaffDetails (Supervisor varchar(100))
create table StaffSupervisors (Supervisor varchar(100))
 
insert into staffdetails values ('Gary')
insert into staffdetails values ('Gary')
insert into staffdetails values ('Mark')
insert into staffdetails values ('Tony')
insert into staffdetails values ('Tony')
 
insert into staffsupervisors values ('Gary')  
insert into staffsupervisors values ('Mark')  
 
select distinct supervisor
  from staffdetails
 where staffdetails.supervisor not in (select supervisor from staffsupervisors)
 
drop table StaffDetails
drop table StaffSupervisors
           
         

Open in New Window

04.16.2008 at 10:35AM PDT, ID: 21370123

Wedmore:

That makes me wonder if there is something about the SQL Server setup we have here. Lets face it, if the left outer join works, there must be a reason for the subquery not to work.

I also just found something else crazy in another table....

SELECT Manager FROM StaffManagers WHERE Manager LIKE 'L%'

All of the names returned started with L except one of the rows was "G.Lansky"

I wasnt aware that the wildcard would also be affective after the fullstop.

Note: Not a new or separate question, my original question still stands - why does the subquery work when the left outer join doesnt.

04.16.2008 at 10:42AM PDT, ID: 21370176

Rank: Wizard

ee_rlee:

>All of the names returned started with L except one of the rows was "G.Lansky"
Why are you expecting "G.Lansky" to be returned? It starts with G

>why does the subquery work when the left outer join doesnt.
I think you meant "left outer join works but subquery doesn't". Have you tried the code I posted? Is it returning any records?

04.16.2008 at 11:44AM PDT, ID: 21370742

Wedmore:

>>Why are you expecting "G.Lansky" to be returned? It starts with G
Thats what I mean - i dont expect it, I dont know why it is being returned. My only assumption is that its because of the fullstop.

>> "left outer join works but subquery doesn't". Have you tried the code I posted? Is it returning any records?

Correct sorry about that. Yes I tried it, even copied and pasted, and it returns zero results. The subquery just doesnt seem to take to "NOT IN".

04.16.2008 at 12:34PM PDT, ID: 21371196

Rank: Genius

ScottPletcher:

NULL value(s) can cause havoc in NOT IN (and sometimes IN). Please try this:

insert into staffsupervisors (supervisor)
select distinct supervisor
from staffdetails
where supervisor not in (select supervisor from staffsupervisors where supervisor is not null)

Accepted Solution

04.16.2008 at 01:02PM PDT, ID: 21371430

Wedmore:

Bingo! Wow - NULL values is really that evil. I knew that concatenating with NULLS causes issues - well it just outputs NULL, but didnt think this would cause an issue. Then again, I didnt think the subquery is that much different to a join (in terms of building its table for the comparison).

ScottPletcher

04.16.2008 at 01:11PM PDT, ID: 21371514

>> NULL values is really that evil. <<

Yes, they are for NOT IN / IN.

But it's logical in its own way.

A comparison of anything to NULL always yields "unknown" (essentially). Note that NOT unknown is also unknown.

On the other hand, a WHERE condition must be *TRUE* for a row to be included.

So if the comparison:

where supervisor not in (...)

returns "unknown", then the row will *not* be selected, because the condition is not *specifically true*.

dportas

04.17.2008 at 07:32PM PDT, ID: 21382906

"A comparison of anything to NULL always yields "unknown" (essentially)."

But not always.

x IN (...) can return TRUE even if the (...) expression list contains a NULL
x IS NULL returns TRUE if x is NULL

There are other exceptions too.

The designers of SQL tried hard to come up with some natural and consistent rules for handling three value logic - but they failed. SQL's handling of NULLs is neither intuitive nor particularly logical. So to achieve useful results with NULLs you need to learn about the quirks and live with them, which is no small task. The alternative is to avoid NULLs altogether, something which SQL unfortunately makes rather difficult because they tend to crop up in results even if you make all your columns non-nullable.

ScottPletcher

04.18.2008 at 06:49AM PDT, ID: 21385685

>> x IN (...) can return TRUE even if the (...) expression list contains a NULL <<

It *might*, or it might not, depending on where the searched for value and the NULL are in the list.

That's way too "flighty" to risk in actual use. When using IN and NOT IN, one should **always** insure that a NULL(s) do not appear in the value list.

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