sql server - SQL query issue in avoid duplicates in INSERT INTO SELECT? -

the following query works perfectly,

insert [egallery].dbo.[customerdetails]  select distinct b.countyb 'mobile' ,  cast(buildingb varchar(100)) 'email' ,  a.cardcode , a.cardname 'first name' , '' 'last name' ,  '' gender , cast(a.address varchar(1000)) 'address' , convert(varchar(10), a.u_birthday,105) 'birthday' ,  convert(varchar(10), a.u_annivday ,105) 'anniversary' ,  case  when a.cardcode '%%'+ c.whscode +'%%'  convert(varchar(10) , a.docdate ,105)  else convert(varchar(10), (select x.createdate ocrd x x.cardcode = a.cardcode) ,105) end 'joindate' ,  c.whscode 'joinstore','open' status ,(select getdate()) createddatetime,(select getdate()) processdatetime, '' statusmsg  oinv  inner join inv12 b on a.docentry = b.docentry  inner join inv1 c on a.docentry = c.docentry  c.linenum = '0'  --b.countyb not in(select d.mobile [egallery].dbo.[customerdetails] d d.mobile=b.countyb) --not exists (select mobile [egallery].dbo.[customerdetails] d d.mobile=b.countyb) 

but before insert records [egallery].dbo.[customerdetails] table, need check whether phone number exists in table. if record exists, there no need insert again. have added 1 more condition (which have commented out in query) reports error while running query:

cannot resolve collation conflict between "sql_latin1_general_cp850_ci_as" , "latin1_general_ci_ai" in equal operation. 

according here have add collate database_default queries this:

where c.linenum = '0' , b.countyb not in(select d.mobile [egallery].dbo.[customerdetails] d d.mobile collate database_default = b.countyb collate database_default) , not exists (select mobile [egallery].dbo.[customerdetails] d d.mobile collate database_default = b.countyb collate database_default)