There are two ways to delete data from the table.
DELETE FROM [dbo].[TT2_COPY] WHERE id < 1000 -- deletes selected rows TRUNCATE TABLE [dbo].[TT2_COPY] -- deletes all rows
a) is slow,
b) you can remove selected (not all) rows,
c) deletion can be reversed.
a) is faster,
b) deletes all rows, where clause is not supported,
c) cannot be reversed,
d) triggers are not executed,
e) when foreign key references the table it will fail,
f) alter table privilege is neccessary
g) identity is zeroed.