Tuesday, February 19, 2013

Using Foreign Keys to Determine Table Insertion Order

Here's a script to determine, based on your database's foreign key relationships, what the insertion order would be for, say, a testing dataset.

      with cteFK (pktable, fktable) as ( 
            pktable = s1.name + '.' + o1.name 
       ,    fktable = isnull(s2.name + '.' + o2.name, '')        
       from sys.objects o1       
       left outer join sys.sysforeignkeys fk on o1.object_id = fk.fkeyid        
       left outer join sys.objects o2 on o2.object_id = fk.rkeyid        
    left outer join sys.schemas s1 on o1.schema_id = s1.schema_id
    left outer join sys.schemas s2 on o2.schema_id = s2.schema_id
       where o1.type_desc = 'user_table'       
       and o1.name not in ('dtproperties','sysdiagrams')        
       group by s1.name + '.' + o1.name 
      , isnull(s2.name + '.' + o2.name, '')       
), cteRec (tablename, fkcount) as  ( 
       select tablename = pktable 
       ,    fkcount = 0
       from cteFK    
       UNION ALL       
    select tablename = pktable 
       , fkcount = 1
       from cteFK  
       cross apply cteRec        
       where cteFK.fktable = cteRec.tablename    
       and cteFK.pktable <> cteRec.tablename
, InsertOrder = dense_rank() OVER ( ORDER BY max(fkcount) asc )
from (       
              tablename = fktable
       ,      fkcount = 0 
       from cteFK 
       group by fktable    
       UNION ALL    
       select tablename = tablename, fkcount = sum(ISNULL(fkcount,0))   
       from cteRec      
       group by tablename
     ) x 
where x.tablename <> ''
group by tablename 
order by InsertOrder asc, TableName asc

Use the sample script from the previous post on how to "Script Out Foreign Keys With Multiple Keys" for an example of building a complicated set of foreign key relationships to test this script out.

Here's the results from that example:

Similarly, this script would generate an order for you to unravel the data - the numbers descending would allow you to delete in the proper order,
delete from fktable11
delete from fktable10
delete from fktable9
delete from fktable8
delete from fktable6
delete from fktable4
delete from fktable2
delete from fktable7
delete from fktable5
delete from fktable3
delete from fktable1
... or drop the tables in the proper order.
drop table fktable11
drop table fktable10
drop table fktable9
drop table fktable8
drop table fktable6
drop table fktable4
drop table fktable2
drop table fktable7
drop table fktable5
drop table fktable3
drop table fktable1
UPDATED 20140507: changed old system reference objects (sysobjects) to new system reference objects (sys.objects) UPDATED 20140624: added "and cteFK.pktable <> cteRec.tablename", see comments for explanation.


Ross said...

I get "The statement terminated. The maximum recursion 100 has been exhausted before statement completion."
My database only has 24 tables in it.

Ross said...

Ah, I had a table with a FK to itself. This and other loops will kill your script ... of course, there's no easy way to say how to actually do an insert if there is a loop.

w said...

Actually, adding the line "and cteFK.pktable <> cteRec.tablename" seemed to clear up that case. Thanks for commenting!