Best Practices for SAP BI using DB2 9 for z/OS - IBM Redbooks

Table 10-2 Indexing options
Column Local
or join
AND "/BIC/AZOSASALE00"."ACCNT_ASGN" IN ('00', '01', '04', '06')
AND "/BIC/AZOSASALE00"."CALMONTH" BETWEEN '200311' AND '200404'
AND "/BIC/AZOSASALE00"."CURTYPE" = 'B0'
For the non-leading tables in the join, local predicates and join predicates are
treated equally from the perspective of the ability to match index columns. Equal
and IN predicates must precede range (BETWEEN, LIKE, =)
predicates in the index, however, since range predicates will stop the index
matching, and subsequent predicates will be applied as index screening.
Similarly, a second IN predicate will also force matching to stop (at the column
immediately preceding the second IN list) and revert to index screening.
Therefore, where possible, priority should be given to equal predicates for
indexing.
Whether local predicates appear before join predicates depends on whether the
local predicates will always appear in the query. If so, then the preference is to
order local equal and IN columns before join columns in the index. This allows
these columns to be used as matching as the leading or non-leading table in a
join.
Also, local predicates as the leading columns will ensure that any matching
access to this index (as leading or non-leading table) will be restricted to the
bounds of the equal predicate, which can provide a better bufferpool hit ratio and
exploitation of index lookaside.
To improve flexibility of local predicates, an alternative is to partition by a
commonly used local predicate. A good example is often a time-based column in
a data warehouse environment. Data warehouses (including SAP BI DSO and
InfoCubes) generally contain many months or years of data, but users often
query only the most recent, thus making separation of current and historical
(using partitioning) a wise choice.
The indexing options for table /BIC/AZOSASALE00 are shown in Table 10-2.
Operator Partition
candidate
Index
column
sequence
CURTYPE Local = Possibly 1 Optional
ACCT_ASGN Local IN No 2 Optional
Mandatory/optional
/BIC/ZMATLPLNT Join = No 3 Mandatory
PLANT Join = No 4 Mandatory
Chapter 10. Tips for SQL efficiency 221