Select query with secondary index

Question

hi,
i have a report which is giving performance issues on a perticular select query on KONH table.
the select query doesnt use the primary key fields and table already has around 19 million entries.So there was a secondary index created for the fields in the table.
now, KONH is a client specific table, and hence has MANDT as the first field. when the table is not indexed it is sorted according to the order of fields, like first MANDT, then primary key fields and then remaining fields.. (correct me if i am wrong)
but the secondary index created doesnt has MANDT in it..(yea, a mistake! )...
but instead of correccting the secondary index, i am told to change the select query..
so, i used a "client specific" syntax to sort the issue.. but i dont understand whre i should put the "where mandt eq sy-mandt" clause..
should i put it right after all my secondary index fields are over? or what happens to the order of fields which are not present in the list of secondary index?
kindaly help.
thanx.

Answer 1

Hi chinmay kulkarni,
its better if you can ask concerned person to add MANDT field in your  index as well....
Indexes and MANDT
If a table begins with the mandt field, so should its indexes. If a table begins with mandt and an index doesn't, the optimizer might not use the index.
Remember, if you will, Open SQL's automatic client handling feature. When select * from ztxlfa1 where land1 = 'US' is executed, the actual SQL sent to the database is select * from ztxlfa1 where mandt = sy-mandt and land1 = 'US'. Sy-mandt contains the current logon client. When you select rows from a table using Open SQL, the system automatically adds sy-mandt to the where clause, which causes only those rows pertaining to the current logon client to be found.
When you create an index on a table containing mandt, therefore, you should also include mandt in the index. It should come first in the index, because it will always appear first in the generated SQL.
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.)
For Example...
SELECT KUNNR KUNN2 INTO TABLE T_CUST_TERR
FROM KNVP CLIENT SPECIFIED
WHERE MANDT = SY-MANDT " here MANDT shd be first
AND KUNN2 IN S_TERR
AND PARVW LIKE 'Z%'.
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
Also pls have a look on below link
http://www.sapfans.com/sapfans/forum/devel/messages/30240.html
Hope it will solve your problem..
Reward points if useful...
Thanks & Regards
ilesh 24x7