Question

I have a table in an oracle database with 15 fields.
This table had 3500000 inserts. I deleted them all.

delete
from table

After that, whenever I execute a select statement
I get a very slow response (7 sec) even though the table is empty.
I get a normal response only in the case that I search
according to an indexed field.

Why?

Answer 1

As Gritem says, you need to understand high water marks etc

If you do not want to truncate the table now (because fresh data has been inserted), use alter table xyz shrink space documented here for 10g