Using Join Indexes; Allowing Enough Disk Space For Deletions - Sybase Adaptive Server IQ 12.4.2 Administration And Performance Manual

Using join indexes

Allowing enough disk space for deletions

You should create either an
each column referenced by the
IQ cannot guarantee that its query optimizer will produce the best execution
plan if some columns referenced in the
index. Non-aggregated columns referenced in the
have the or index in addition to the default index. For example:
LF HG
SELECT c.name, SUM(l.price * (1 - l.discount))
FROM customer c, orders o, lineitem l
WHERE c.custkey = o.custkey
AND o.orderkey = l.orderkey
AND o.orderdate >= "1994-01-01"
AND o.orderdate < "1995-01-01"
GROUP by c.name
HAVING c.name NOT LIKE "I%"
AND SUM(l.price * (1 - l.discount)) > 0.50
ORDER BY 2 desc
In addition to the default index, all columns in this example beside
should have an
l.discount
Users frequently need to see the data from more than one table at once. This
data can be joined at query time, or in advance by creating a join index. You
can usually improve query performance by creating a join index for columns
that must be joined in a consistent way.
Because join indexes require substantial time and space to load, you should
create them only for joins needed on a regular basis. Adaptive Server IQ join
indexes support one-to-many and one-to-one join relationships.
When you delete data rows, Adaptive Server IQ creates a version page for each
database page that contains any of the data being deleted. The versions are
retained until the delete transaction commits. For this reason, you may need to
add disk space when you delete data. See "Overlapping versions and
deletions" for details.
CHAPTER 12 Managing System Resources
or index in addition to the default index on
LF HG
clause in a join query. Adaptive Server
WHERE
clause lack either an
WHERE
or index.
LF HG
or
LF HG
clause must also
HAVING
and
l.price
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