Function slows the select

Hi,

In the following select statement I have a function "GetSid" that slows the
update for hours even if the Link_keszit updatable table consists of a few rows.

 Update 

UpdateTable--Varosokat
updatel
   Set UpdateTable_Column1=

--


      (

        Select

distinct  'Some string here'||GetSid||UpdateTable_Column2||Logo.Logo_Filenev


         

         From VarosTorzs,Logo, Link_keszit

         

         Where

          logo_varos_unique_az  = link_keszit_varos_az 

          

          and logo.logo_azonosito1= 'KKEPX' and logo.logo_azonosito2= '20200'

          

          and logo_varos_unique_az  = varos_unique_azonosito

       

           ) 

         

     Where UpdateTable_Column2 Is Not Null ;


The GetSid function is:

CREATE OR REPLACE Function GetSid Return VarChar2 AS


 BEGIN

   return(SYS_GUID());

 END GetSid;



So the problem is that _with_ GetSid function it takes many hours instead of a few minutes.


Thank you in advance

Zsolt Csillag,
Hungary