I want information in practical sceario how to create indexes?

Question

hi,
i want complete information about indexes? how create indexes in real time?

Answer 1

" Secondary Database
First it must be stated that table design is a more logical work while index design is rather technical. In table design it might make sense to place certain fields (client, company code, ...) in the beginning. In index design, this is not advisable.  Very important for an index is that it contains very selective fields in the beginning. Those are fields like object numbers. Not selective are client, company code, ... 
Indexes should be small (few fields).  The Database optimizer can combine two or more indexes to execute a query. 
Indexes of one table should be disjoint (have few common fields), in order not to confuse the optimizer which index to use. 
Note that each index slows the inserts into the table down. Updates are only slowed down if indexed fields are updated. In general, heavy inserted tables should have only few indexes while heavy selected tables might have more. 
" Creating Secondary Indexes
Procedure
1.In the maintenance screen of the table, choose Indexes.
If indexes already exist on the table, a list of these indexes is displayed. Choose .
2.In the next dialog box, enter the index ID and choose 
The maintenance screen for indexes appears.
3.Enter an explanatory text in the field Short text.
You can then use the short text to find the index at a later time, for example with the R/3 Repository Information System.
4.Select the table fields to be included in the index using the input help for the Field name column.
The order of the fields in the index is very important. See What to Keep in Mind for Secondary Indexes.
5.If the values in the index fields already uniquely identify each record of the table, select Unique index.
A unique index is always created in the database at activation because it also has a functional meaning (prevents double entries of the index fields).
6.If it is not a unique index, leave Non-unique index selected.
In this case you can use the radio buttons to define whether the index should be created for all database systems, for selected database systems or not at all in the database.
7.Select for selected database systems if the index should only be created for selected database systems.
Click on the arrow behind the radio buttons. A dialog box appears in which you can define up to 4 database systems with the input help. Select Selection list if the index should only be created on the given database systems. Select Exclusion list if the index should not be created on the given database systems. Choose .
8.Choose  activate.
" Result
The secondary index is automatically created in the database during activation if the corresponding table was already created there and index creation was not excluded for the database system.
You can find information about the activation flow in the activation log, which you can call with Utilities ® Activation log. If errors occurred when activating the index, the activation log is automatically displayed.
" How to Check if an Index is Used
Procedure
1.Open a second session and choose System -> Utilities ->Performance trace.
The Trace Requests screen appears.
2.Select Trace on.
The SQL trace is activated for your user, that is all the database operations under your user are recorded.
3.In the first window, perform the action in which the index should be used.
If your database system uses a cost-based optimizer, you should perform this action with as representative data as possible. A cost-based optimizer tries to determine the best index based on the statistics.
4.In the second session, choose Trace off and then Trace list.
Result
The format of the generated output depends on the database system used. You can determine the index that the database used for your action with the EXPLAIN function for the critical statements (PREPARE, OPEN, REPOPEN).
" What to Keep in Mind for Secondary Indexes
How well an existing index supports data selection from a table largely depends on whether the data selected with the index represents the data that will ultimately be selected. This can best be shown using an example.
' Example  :
An index is defined on fields FIELD1, FIELD2, FIELD3 and FIELD4 of table BSPTAB in this order. This table is accessed with the SELECT statement:
SELECT * FROM BSPTAB WHERE FIELD1 = X1 AND FIELD2 = X2 AND FIELD4= X4.
Since FIELD3 is not specified more exactly, only the index sorting up to FIELD2 is of any use. If the database system accesses the data using this index, it will quickly find all the records for which FIELD1 = X1 and FIELD2 = X2. You then have to select all the records for which FIELD4 = X4 from this set.
The order of the fields in the index is very important for the accessing speed. The first fields should be those which have constant values for a large number of selections. During selection, an index is only of use up to the first unspecified field.
Only those fields that significantly restrict the set of results in a selection make sense for an index.
Reward  points if it is usefull.....
Girish