Question

I want to delete all rows in a datatable.
I use something like this:

foreach (DataRow row in dt.Rows)
{
  row.Delete();
}
TableAdapter.Update(dt);

It works good but it takes lots of time if I have much rows.
Is there any way to delete all rows at once?

Answer 1

If you are running your code against a sqlserver database then
use this command

string sqlTrunc = "TRUNCATE TABLE " + yourTableName
SqlCommand cmd = new SqlCommand(sqlTrunc, conn);
cmd.ExecuteNonQuery();

this will be the fastest method and will delete everything from your table and reset the identity counter to zero.

The TRUNCATE keyword is supported also by other RDBMS.

5 years later:
Looking back at this answer I need to add something. The answer above is good only if you are absolutely sure about the source of the value in the yourTableName variable. This means that you shouldn’t get this value from your user because he can type anything and this leads to Sql Injection problems well described in this famous comic strip. Always present your user a choice between hard coded names (tables or other symbolic values) using a non editable UI.