Question

We have already created the database framework, with all the relations and dependencies. But inside the tables were just the dummy data, and we need to get rid of these dummy data, and start adding the correct ones. How can we clear everything and leave the primary keys (IsIdentity: yes) back to zero, and also without affecting the foreign-table relational structure.

Thanks a lot!

Answer 1

You can take the following steps:

-- disable all foreign key constraints
EXEC sp_msforeachtable "ALTER TABLE ? NOCHECK CONSTRAINT all"

-- delete data in all tables
EXEC sp_MSForEachTable "DELETE FROM ?"

-- enable all constraints
exec sp_msforeachtable "ALTER TABLE ? WITH CHECK CHECK CONSTRAINT all"

More on disabling constraints and triggers here

if some of the tables have identity columns we may want to reseed them

EXEC sp_MSforeachtable "DBCC CHECKIDENT ( '?', RESEED, 0)"

Note that the behaviour of RESEED differs between brand new table, and one which had had some date inserted previously from BOL:

DBCC CHECKIDENT (‘table_name’, RESEED, newReseedValue)

The current identity value is set to
the newReseedValue. If no rows have
been inserted to the table since it
was created, the first row inserted
after executing DBCC CHECKIDENT will
use newReseedValue as the identity.
Otherwise, the next row inserted will
use newReseedValue + 1. If the value
of newReseedValue is less than the
maximum value in the identity column,
error message 2627 will be generated
on subsequent references to the table.