indexes

[Former Member]

hi ,

can any one explain me about the indexes

[Former Member]

hi,

There are two kinds of indexes. one is primary index and other one is secondary index.

primary index will be automatically created by the system.

but user has to define this secondary index.

Maximum of 15 secondary index is possible.(As per 21 days book).

but keep the secondary index as minimum as possible.

reward points if useful,

seshu.

[Former Member]

Hi,

Refer this.

Thanks,

Anitha

[Former Member]

Hi,

An index can be considered a copy of a database table that has been reduced to certain fields. This copy is always in sorted form. Sorting provides faster access to the data records of the table, for example using a binary search. The index also contains a pointer to the corresponding record of the actual table so that the fields not contained in the index can also be read.

The primary index is distinguished from the secondary indexes of a table. The primary index contains the key fields of the table and a pointer to the non-key fields of the table. The primary index is created automatically when the table is created in the database

You can also create further indexes on a table in the ABAP Dictionary. These are called secondary indexes. This is necessary if the table is frequently accessed in a way that does not take advantage of the sorting of the primary index for the access.

Indexes speed up data selection from the database. They consist of selected fields of a table, of which a copy is then made in sorted order. If you specify the index fields correctly in a condition in the WHERE or HAVING clause, the system only searches part of the index (index range scan).

The system automatically creates the primary index. It consists of the primary key fields of the database table. This means that for each combination of fields in the index, there is a maximum of one line in the table. This kind of index is also known as UNIQUE.

If you cannot use the primary index to determine the result set because, for example, none of the primary index fields occur in the WHERE or HAVINGclauses, the system searches through the entire table (full table scan). For this case, you can create secondary indexes, which can restrict the number of table entries searched to form the result set.

You create secondary indexes using the ABAP Dictionary. There you can create its columns and define it as UNIQUE. However, you should not create secondary indexes to cover all possible combinations of fields.

Only create one if you select data by fields that are not contained in another index, and the performance is very poor. Furthermore, you should only create secondary indexes for database tables from which you mainly read, since indexes have to be updated each time the database table is changed. As a rule, secondary indexes should not contain more than four fields, and you should not have more than five indexes for a single database table.

If a table has more than five indexes, you run the risk of the optimizer choosing the wrong one for a particular operation. For this reason, you should avoid indexes with overlapping contents.

Secondary indexes should contain columns that you use frequently in a selection, and that are as highly selective as possible. The fewer table entries that can be selected by a certain column, the higher that column’s selectivity. Place the most selective fields at the beginning of the index. Your secondary index should be so selective that each index entry corresponds to, at most, five percent of the table entries. If this is not the case, it is not worth creating the index. You should also avoid creating indexes for fields that are not always filled, where their value is initial for most entries in the table.

If all of the columns in the SELECT clause are contained in the index, the system does not have to search the actual table data after reading from the index. If you have a SELECT clause with very few columns, you can improve performance dramatically by including these columns in a secondary index.

What is the difference between primary index and secondary index?

http://help.sap.com/saphelp_47x200/helpdata/en/cf/21eb2d446011d189700000e8322d00/frameset.htm

A difference is made between Primary & Secondary indexes to a table. the primary index consists of the key fields of the table and a pointer to the non-keys-fields of the table. The Primary index is generated automatically when a table is created and is created in the datebase as the same times as the table. It is also possible to define further indexes to a table in the ABAP/4 dictionary, which are then referred to as Secondary indexes.

Always it is not mandatory that an index should have all the key fields of a table. To see the index of a table

goto SE11->specify table name->click on the indexes... button on the application toolbar.

Based on your requirement you can you any of those index fields in the where clause of your query. Always its a better practice to use the index fields in the order specified. While selecting the records from a table it is always better to select the fields in the same order as specified in the table.

go thru this: http://sap.ittoolbox.com/documents/popular-q-and-a/specifying-the-index-to-be-used-2462

Regards,

Priyanka.

[Former Member]

Hi,

<b>Check the Indexes in this help</b>

http://help.sap.com/saphelp_470/helpdata/en/cf/21eb20446011d189700000e8322d00/frameset.htm

Regards,

Ranjit Thakur.

<b>Please Mark The Helpful Answer.</b>

[Former Member]

Hi,

Indexes speed up data selection from the database. They consist of selected fields of a table, of which a copy is then made in sorted order. If you specify the index fields correctly in a condition in the WHERE or HAVING clause, the system only searches part of the index (index range scan). The primary index is always created automatically in the R/3 System. It consists of the primary key fields of the database table. This means that for each combination of fields in the index, there is a maximum of one line in the table. This kind of index is also known as UNIQUE. If you cannot use the primary index to determine the result set because, for example, none of the primary index fields occur in the WHERE or HAVING clause, the system searches through the entire table (full table scan). For this case, you can create secondary indexes, which can restrict the number of table entries searched to form the result set. You specify the fields of secondary indexes using the Abap Dictionary. You can also determine whether the index is unique or not. However, you should not create secondary indexes to cover all possible combinations of fields. Only create one if you select data by fields that are not contained in another index, and the performance is very poor. Furthermore, you should only create secondary indexes for database tables from which you mainly read, since indexes have to be updated each time the database table is changed. As a rule, secondary indexes should not contain more than four fields, and you should not have more than five indexes for a single database table. If a table has more than five indexes, you run the risk of the optimizer choosing the wrong one for a particular operation. For this reason, you should avoid indexes with overlapping contents. Secondary indexes should contain columns that you use frequently in a selection, and that are as highly selective as possible. The fewer table entries that can be selected by a certain column, the higher that column's selectivity. Place the most selective fields at the beginning of the index. Your secondary index should be so selective that each index entry corresponds to at most five percent of the table entries. If this is not the case, it is not worth creating the index. You should also avoid creating indexes for fields that are not always filled, where their value is initial for most entries in the table. If all of the columns in the SELECT clause are contained in the index, the system does not have to search the actual table data after reading from the index. If you have a SELECT clause with very few columns, you can improve performance dramatically by including these columns in a secondary index.

http://help.sap.com/saphelp_470/helpdata/en/cf/21eb20446011d189700000e8322d00/frameset.htm

Regards

Sudheer

[Former Member]

to reduce DB cost on the Huge DB tables , we have to create Se.Indexes.

u can maintain upto 7 S,Indexes on any Trans.Tables.

Regards

Peram