delete all from table
You can use the below query to remove all the rows from the table, also you should keep it in mind that it will reset the Identity too.
TRUNCATE TABLE table_name
This should be faster:
DELETE * FROM table_name;
because RDBMS don't have to look where is what.
You should be fine with truncate though:
truncate table table_name
This is deletes the table table_name.
Replace it with the name of the table, which shall be deleted.
DELETE FROM table_name;