ABAP Development

[Former Member]

Hi All,

I'm bit bemused when to use Primary Index & Secondary Index.

Can any one help me about my this ?

Thanks and Regards,

Noor

[Former Member]

Hi,

Primary and secondary indexes

Index: Technical key of a database table.

Primary index: 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.

Secondary index: Additional indexes could be created considering the most frequently accessed dimensions of the table.

Structure of an Index

An index can be used to speed up the selection of data records from a table.

An index can be considered to be a copy of a database table reduced to certain fields. The data is stored in sorted form in this copy. This sorting permits fast access to the records of the table (for example using a binary search). Not all of the fields of the table are contained in the index. The index also contains a pointer from the index entry to the corresponding table entry to permit all the field contents to be read.

When creating indexes, please note that:

An index can only be used up to the last specified field in the selection! The fields which are specified in the WHERE clause for a large number of selections should be in the first position.

Only those fields whose values significantly restrict the amount of data are meaningful in an index.

When you change a data record of a table, you must adjust the index sorting. Tables whose contents are frequently changed therefore should not have too many indexes.

Make sure that the indexes on a table are as disjunctive as possible.

(That is they should contain as few fields in common as possible. If two indexes on a table have a large number of common fields, this could make it more difficult for the optimizer to choose the most selective index.)

Accessing tables using Indexes

The database optimizer decides which index on the table should be used by the database to access data records.

You must distinguish between the primary index and secondary indexes of a table. The primary index contains the key fields of the table. The primary index is automatically created in the database when the table is activated. If a large table is frequently accessed such that it is not possible to apply primary index sorting, you should create secondary indexes for the table.

The indexes on a table have a three-character index ID. '0' is reserved for the primary index. Customers can create their own indexes on SAP tables; their IDs must begin with Y or Z.

If the index fields have key function, i.e. they already uniquely identify each record of the table, an index can be called a unique index. This ensures that there are no duplicate index fields in the database.

When you define a secondary index in the ABAP Dictionary, you can specify whether it should be created on the database when it is activated. Some indexes only result in a gain in performance for certain database systems. You can therefore specify a list of database systems when you define an index. The index is then only created on the specified database systems when activated

Regards,

Shiva Kumar

[Former Member]

Thanks shiva,

Your explanation was such great that my concept is clear.

regards

noor.

[Former Member]

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|http://help.sap.com/saphelp_nw70/helpdata/en/cf/21eb20446011d189700000e8322d00/frameset.htm]

I hope it helps.

Best Regards,

Vibha

Please mark all the helpful answers

[Former Member]

Thanks Vibha for your valuable inputs, this helped me a lot.

[Former Member]

hi,

You can search a table for data records that satisfy certain search criteria faster using an index.

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.

Table SCOUNTER in the flight model contains the assignment of the carrier counters to airports. The primary index on this table therefore consists of the key fields of the table and a pointer to the original data records.

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. Different indexes on the same table are distinguished with a three-place index identifier.

All the counters of carriers at a certain airport are often searched for flight bookings. The airport ID is used to search for counters for such an access. Sorting the primary index is of no use in speeding up this access. Since table SCOUNTER has a large number of entries, a secondary index on the field AIRPORT (ID of the airport) must be created to support access using the airport ID.

pls reward if helpful.

[Former Member]

Helllo Shiva Kumar ,

You have specified that there are database sytems where to which we can assign secondary .index .

Can u please elaborate in this as we generally have one Database system.

Thanks

[Former Member]

Hi,

When creating indexes, please note that:

An index can only be used up to the last specified field in the selection! The fields which are specified in the WHERE clause for a large number of selections should be in the first position.

Only those fields whose values significantly restrict the amount of data are meaningful in an index.

When you change a data record of a table, you must adjust the index sorting. Tables whose contents are frequently changed therefore should not have too many indexes.

Make sure that the indexes on a table are as disjunct as possible.

The database optimizer decides which index on the table should be used by the database to access data records.

You must distinguish between the primary index and secondary indexes of a table. The primary index contains the key fields of the table. The primary index is automatically created in the database when the table is activated. If a large table is frequently accessed such that it is not possible to apply primary index sorting, you should create secondary indexes for the table.

The indexes on a table have a three-character index ID. '0' is reserved for the primary index. Customers can create their own indexes on SAP tables; their IDs must begin with Y or Z.

If the index fields have key function, i.e. they already uniquely identify each record of the table, an index can be called a unique index. This ensures that there are no duplicate index fields in the database.

When you define a secondary index in the ABAP Dictionary, you can specify whether it should be created on the database when it is activated. Some indexes only result in a gain in performance for certain database systems. You can therefore specify a list of database systems when you define an index. The index is then only created on the specified database systems when activated.

Regards,

vineela

[Former Member]

Hi,

You can use primary index in the where condition provided you have values to compare

say for eg: where ebeln in so_ebeln and pr_date = '12.05.2008'.

if can give where conditions on the key fields of the table then primary index comes into picture..

(primary index will help in faster data access).

if no prmary index is available say for field by name 'AGE' you can create ur own indes in SE11. bt u may have to consult your BASIS admin before doing so.

for large tables avoid creating indices.

AS FAR AS POSSIBLE USE PRIMARY INDEX.

I hope this helps you.