Copying a row in SQL is easy:
select * into newTable from oldtable, and other variations.
But what if you want to copy tables that have foreign keys pointed to that row? For example, say you have a [users] table, and a [user_preferences] table with a foreign key pointing to [users].
Here, I'll show you how to do this without writing out code for all the tables you want to copy yourself.
In order to use this code, you'll need a special aggregate function,
strconcat. You can create your own easily in the CLR; check out this page for more details.
Using the code
To use this procedure, call it as follows:
declare @oldId bigint, @newId bigint
set @oldId = 60000
where id= @oldId
alter table #usersToClone
drop column id
insert into users
select * from #usersToClone
set @newId = scope_identity()
create table #table_ExcludeFromCloning(
exec table_CloneChildrenOfRow 'users', 'dbo', @oldId, @newId
How it works - recursion and other tricks in SQL
In order to automatically find rows of foreign key tables, we need to use a few tricks. Here are four of the biggest ones:
- First off, we need to get the foreign keys that point to a table. Fortunately, SQL Server has a Stored Procedure,
sp_fkeys, that we can use for just that purpose.
- Second, once we get that list of foreign key tables, we need to execute SQL on each one. Here, we use
sp_executesql to run SQL that we dynamically create.
- Third, our code is recursive SQL - we have one procedure that copies all the foreign key references pointing to a row, and another that copies all the rows for just one of those foreign key tables. They have to call each other, as a foreign key table may have its own primary key!
- Fourth, we have an interesting problem - how do we pass a table from one procedure to another? Table-valued parameters would help, but they're only in SQL Server 2008. In this case, we have to use some tricks with temp tables and table variables. Keep in mind that table variables only have scope within the current procedure, and temp tables have scope in the entire call stack - we have to use both!
Points of interest
This code works for simple tables with multiple foreign key tables referencing them, but there are certain weird scenarios (circular references, for example) that will break it.
If you have the luxury of working with an ORM, I suggest exploring that first before going this route. :)
Contact me with requests and updates!
Something not working? I've only tested this code on our local environment. Gmail me at chris.magradar.
- Latest update - 16 Apr 2010 - new version adds support for different table owners.
- First version - 30 Mar 2010.
Startup web developer, playing around with .NET, T-SQL, and other technologies.