Data in Table which have foreign key relationships are not deleted so first Disable all the constraints and delete all the recode and then Re-enable constraints.

-- Disable all 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"

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

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