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Adaptive Server IQ index types
Advantages and disadvantages of Low_Fast
Comparison with other indexes
Additional indexes
The High_Group (HG) index type
Recommended use
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The following table lists advantages and disadvantages of Low_Fast indexes.
Table 4-5: LF advantages/disadvantages
Advantages
This index is fast, especially for single
table
,
,
,
SUM
AVG
COUNT
,
, and
DISTINCT
MIN
MAX
HNG / HG
The main factor to consider is the number of unique values within
a column. Use
if the number is low.
LF
The
index type may also be appropriate for a
High_Non_Group
column.
Note
It is almost always best to use an
is low (less than 1,000). Consider this index first, if the column appears in the
clause. Only when the number of unique values is high should other
WHERE
indexes (
and
) be considered. For range queries with a high number of
HG
HNG
unique values, also consider having an
The High_Group index is commonly used for join columns with integer data
types. It is also more commonly used than High_Non_Group because it
handles
efficiently.
GROUP BY
Use an
index when:
HG
•
The column will be used in a join predicate
•
A column has more than 1000 unique values
Disadvantages
Can only be used for a maximum of
10,000 unique values.
COUNT
operations.
Cannot use this index if data in your
columns is
BIT
bytes.
index if the number of unique values
LF
index.
HNG
, or
> 255
VARCHAR
Low_Fast
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