Table of Contents
Advertisement
Adaptive Server IQ index types
The High_Non_Group (HNG) index type
Recommended use
Advantages and disadvantages of High_Non_Group
148
However, because multi-column primary keys are always unenforced, the
automatically created High_Group index for a multi-column primary key is a
phantom index: it includes all of the key columns, but does not contain any
data. This structure is used for query optimization, but not for resolving
queries. You need to create explicitly an
primary key columns that will be used in a join predicate.
Add an
index when you need to do range searches.
HNG
An
index requires approximately three times less disk space than an
HNG
index requires. On that basis alone, if you do not need to do group operations,
use an
index instead of a
HNG
Conversely, if you know you are going to do queries that a
more efficiently, or if the column is part of a join and/or you want to enforce
uniqueness, use a
index.
HG
Using the
index in place of a
Note
HNG
performance of complex ad-hoc queries joining four or more tables. If query
performance is important for such queries in your application, choose
instead of
.
HNG
Use an
index when:
HNG
•
The number of unique values is high (greater than 1000)
•
You don't need to do
See the following table for advantages and disadvantages of using a
High_Non_Group index.
(or
) index on any multi-column
HG
LF
index.
HG
index may seriously degrade
HG
on the column
GROUP BY
HG
index handles
HG
HG
Advertisement
Table of Contents
