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

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'