In SQL Server 2005, can I do a cascade delete without setting the property on my tables?

Question

I have a database full of customer data. It's so big that it's really cumbersome to operate on, and I'd rather just slim it down to 10% of the customers, which is plenty for development. I have an awful lot of tables and I don't want to alter them all with "ON DELETE CASCADE", especially because this is a one-time deal.

Can I do a delete operation that cascades through all my tables without setting them up first? If not, what is my best option?

Answer 1

I usually just hand write the queries to delete the records I don't want and save that as a .sql file for future reference. The pseudocode is:

1. select id's of records from the main table that I want to delete into a temp table
2. write a delete query for each related table which joins to the temp table.
3. write a delete query for the main table joining to my temp table.

Answer 2

My suggestion is to go ahead and write a script that will add the on delete cascade to each relationship in the database while exporting a list of modified relationships. Then you can reverse the process and remove the on delete cascade command on each table in the list.

Answer 3

Personally if you are going to leave the records in production, I would also leave them in development. Otherwise you may write code that works fine when the recordset is small but times out when faced with the real recordset.

But if you are determined to do this, I would copy the id field of the records you want to dete from the main table first to a work table. Then I would take each related table and write a delete joining to that worktable to only delete those records. Finish up with the parent table. Make sure this ia written in a script and saved so the next time you want to do a similar thing to your test data, you can easily run it without having to figure out what are the reated tables that need records deleted from them.

Answer 4

Go into SQL Server Management Studio and right-click the database. Select Tasks->Generate Scripts. Click Next twice. On the Options window choose set it to generate CREATE statements only, and put everything to False except for the Foreign Keys. Click Next. Select Tables and Click Next again. Click the "Select All" button and click Next then Finish and send the script to your choice of a query window or file (don't use the clipboard, since it might be a big script). Now remove all of the script that adds the tables and you should be left with a script to create your foreign keys.

Make a copy of that script because it is how you'll restore your database to its current state. Use a search and replace to add the ON DELETE CASCADE to the end of each constraint. This might vary depending on how your FKs are currently set up and you might need to do some manual editing.

Repeat the script generation, but this time set it to generate DROP statements only. Be sure to manually remove the table drops that are generated. Run the drops, then run your edited creates to make them all cascade on delete. Do your deletes, run the drop script again and then run the script that you saved off at the start.

Also - MAKE A BACKUP OF YOUR DB FIRST! Even if it's just a dev database, it will save you some headache if part of the script isn't quite right.

Hope this helps!

BTW - you should definitely do some testing with your full test data as another poster suggested, but I can see why you might not need that for initial development. Just don't forget to include that as part of QA at some point.

Answer 5

Unless you want to maintain all related queries as proposed by Chris, the ON DELETE CASCADE is by far the quickest and the most direct solution. And if you don't want it to be permanent, why don't you have some T-SQL code that will switch this option on and off like here

1. remove the original Tbl_A_MyFK constraint (without the ON DELETE CASCADE)

   ALTER TABLE Tbl_A DROP CONSTRAINT Tbl_A_MyFK

2. set the constraint Tbl_A_MyFK with the ON DELETE CASCADE

   ALTER TABLE Tbl_A ADD CONSTRAINT Tbl_A_MyFK FOREIGN KEY (MyFK) REFERENCES (Tbl_B) ON DELETE CASCADE

3. Here you can do your delete

   DELETE FROM Tbl_A WHERE ...

4. drop your constraint Tbl_A_MyFK

   ALTER TABLE Tbl_A DROP CONSTRAINT Tbl_A_MyFK

5. set the constraint Tbl_A_MyFK without the ON DELETE CASCADE

   ALTER TABLE Tbl_A ADD CONSTRAINT Tbl_A_MyFK FOREIGN KEY (MyFK) REFERENCES (Tbl_B)

Answer 6

Combining your advice and a script I found online, I made a procedure that will produce SQL you can run to perform a cascaded delete regardless of ON DELETE CASCADE. It was probably a big waste of time, but I had a good time writing it. An advantage of doing it this way is, you can put a GO statement between each line, and it doesn't have to be one big transaction. The original was a recursive procedure; this one unrolls the recursion into a stack table.

create procedure usp_delete_cascade (
 @base_table_name varchar(200), @base_criteria nvarchar(1000)
)
as begin
 -- Adapted from http://www.sqlteam.com/article/performing-a-cascade-delete-in-sql-server-7
 -- Expects the name of a table, and a conditional for selecting rows
 -- within that table that you want deleted.
 -- Produces SQL that, when run, deletes all table rows referencing the ones
 -- you initially selected, cascading into any number of tables,
 -- without the need for "ON DELETE CASCADE".
 -- Does not appear to work with self-referencing tables, but it will
 -- delete everything beneath them.
 -- To make it easy on the server, put a "GO" statement between each line.

 declare @to_delete table (
  id int identity(1, 1) primary key not null,
  criteria nvarchar(1000) not null,
  table_name varchar(200) not null,
  processed bit not null,
  delete_sql varchar(1000)
 )

 insert into @to_delete (criteria, table_name, processed) values (@base_criteria, @base_table_name, 0)

 declare @id int, @criteria nvarchar(1000), @table_name varchar(200)
 while exists(select 1 from @to_delete where processed = 0) begin
  select top 1 @id = id, @criteria = criteria, @table_name = table_name from @to_delete where processed = 0 order by id desc

  insert into @to_delete (criteria, table_name, processed)
   select referencing_column.name + ' in (select [' + referenced_column.name + '] from [' + @table_name +'] where ' + @criteria + ')',
    referencing_table.name,
    0
   from  sys.foreign_key_columns fk
    inner join sys.columns referencing_column on fk.parent_object_id = referencing_column.object_id 
     and fk.parent_column_id = referencing_column.column_id 
    inner join  sys.columns referenced_column on fk.referenced_object_id = referenced_column.object_id 
     and fk.referenced_column_id = referenced_column.column_id 
    inner join  sys.objects referencing_table on fk.parent_object_id = referencing_table.object_id 
    inner join  sys.objects referenced_table on fk.referenced_object_id = referenced_table.object_id 
    inner join  sys.objects constraint_object on fk.constraint_object_id = constraint_object.object_id
   where referenced_table.name = @table_name
    and referencing_table.name != referenced_table.name

  update @to_delete set
   processed = 1
  where id = @id
 end

 select 'print ''deleting from ' + table_name + '...''; delete from [' + table_name + '] where ' + criteria from @to_delete order by id desc
end

exec usp_delete_cascade 'root_table_name', 'id = 123'