What is the "No database index" means when you Creating Secondary Indexes?

Question

HI,
   I'm Creating Secondary Indexes in the maintenance screen of the table(se11)
   There are three options under "Non-unique Index":
   1.Index on all database systems
   2.For selected database systems
   3.No database index
My questions is :
  What do u mean by "No Database Index" and when is it used.
  Can anybody plz tell me what's the difference of this three options ?
  Here is what i found in the help:
   No database index: The index is not created in the database. If you
   choose this option for an index that already exists in the database,
   it is deleted when you activate this option.

Answer 1

Hi,
It is clear from the help documentation,
Here see what the help document says:
Create the index in the database (selection)
Whether an index improves or worsens performance often depends on the database system. You can therefore set whether an index defined in the ABAP Dictionary should be created in the database.
This makes it easier to install a platform-specific customer system.
You can set this option as follows:
1. Index in all database systems: The index is always created in the database.
2. In selected database systems: The index is created depending on the database system used. In this option, you must specify the databases in which the indexes are to be created. You can do this either on an inclusive (list of systems on which it should be created) or an exclusinve (list of systems on which it should not be created) basis. In either case, you can list up to four different database systems.
3. No database index:: The index is not created in the database. If you set this option for an index that already exists in the database, it is deleted when you activate the table in the ABAP Dictionary.
Note: Unique indexes have an extra function, and must therefore always be created in the database. The database system prevents entries or index fields being duplicated. Since programs may rely on this database function, you cannot delete unique indexes from the database.
Hope it helps you,
Regards,
Abhijit G. Borkar