如何解决 SQL 服务器中的“对象已存在”错误

Question

I'm trying to run a query with a different range of data but for some reason when I run it, it gives back an error stating:

Msg 2714, Level 16, State 6, Line 54
There is already an object named '##contacts' in the database.

How would I get around this? Is it a column or columns in the database that are created and that I need to drop?

Code I'm using:

use KBData
go

declare 
    @startdate datetime='2010-01-01',
    @enddate datetime = '2020-05-26';

/*from contacts*/
select
    lower(c.contactid) as contactid ,
    replace(replace(lower(c.emailaddress1),' ',''),',','') as emailaddress1,
    replace(replace(lower(c.emailaddress2),' ',''),',','') as emailaddress2,
    replace(replace(lower(c.emailaddress3),' ',''),',','') as emailaddress3
into ##contacts
from crm.Contact c
where (c.createdonutc >= @startdate and c.createdonutc < dateadd(dd,1,@enddate))
and (c.emailaddress1 is not null or c.emailaddress2 is not null or c.emailaddress3 is not null)

/*from buyers*/
select 
    lower(b.Email) as email
into #sales
from crm.SalesAgreement s  
left join dbo.BuyerContracts bc
    join dbo.buyers b
    on b.ProspectNo = bc.ProspectNo
    and b.Deleted is null  
    on s.kb_salesagreementnumber = bc.SalesAgreementNo
    and bc.Deleted is null
where (s.kb_saledate >= @startdate and s.kb_saledate < dateadd(dd,1,@enddate))
and s.Deleted is null   ;

select
    distinct replace(replace(lower(b.email),' ',''),',','') as email
into #buyers
from #sales b
where b.Email is not null ;

Answer 1

The issue you're running into stems from your use of a global temporary table ( ##tableName ) rather than a local temporary table ( #tableName ). The two behave differently.

A local temp table is created on the fly, is only accessible from the session where it is created, and is dropped when that session closes it's connection, or unless it is explicitly dropped before that. It's completely contained within that scope.

A global temp table is also created on the fly, but is then accessible via any connection to the server. For instance (and I was just doing this earlier today), you can create a global temp table in one SSMS window, and then work with that table in multiple other SSMS windows. Or someone else from your team can work with it. The table continues to exist until the last session accessing the table is disconnected, or, also, unless it's explicitly dropped before then.

So if you had two sessions open with this code running, the ##contacts from one session would already exist when the second session tries to create it. There are a few situations when you need a global temp table, and you need to do existence checks and such in those sitations, but they're few and far between. It's generally easier to work with local temp tables.