Indexes are described as a copy of a database table reduced
to specific fields. This data exists in sorted form. This
sorting form ease fast access to the field of the tables. In
order that other fields are also read, a pointer to the
associated record of the actual table are included in the
index. the indexes are activated along with the table and
are created automatically with it in the database.

Indexes - What are they and how can I use them? 


An index helps to speed up selection from the database. An 
index is a sorted copy of selected database table fields. 

The primary index is always automatically created in an 
ABAP-based SAP system. It consists of the primary key 
fields of the database table. This means, for each 
combination of the index fields exists a maximum of one 
record in the table. This kind of index is called a UNIQUE 
index. 

If the primary index cannot be used to determine selection 
result, (for example, the WHERE condition does not contain 
any primary index fields), the system searches the whole 
table. To prevent this, and determine the selection result 
by searching through a restricted number of database 
records, you can create a secondary index. 

However, you should not define an index for all possible 
fields in the WHERE condition. 

Creating a secondary index : 


You can use the transaction ABAP Dictionary Change → 
Indexes... → Create to create an index. To make the index 
unique, select UNIQUE. To specify the fields that will 
comprise the index, choose "Choose fields". Then save and 
activate the index. 


Optimal number of indexes for a table : 


You should not create more than five indexes for any one 
table because: 

Whenever you change table fields that occur in the index, 
the index itself is also updated. 
The amount of data increases. 
The optimizer has too many chances to make mistakes by 
using the 'wrong' index. 


If you are using more than one index for a database table, 
ensure that they do not overlap. 

Thank's and Regards
Shreeshail Diggi
SAP Technical Consultant Infinite India