Sybase 12.4.2 - Manual (Page 164)

Adaptive Server IQ index types
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• VARCHAR data with more than 255 bytes
HNG indexes do not allow FLOAT , REAL , or DOUBLE data.
All other data types are supported in all index types.
If you try to create an index on a column that contains VARCHAR data greater
than 255 bytes, you get this error message:
An index cannot be created on a varchar column greater
than 255 characters.
Combining index types
If a column is going to be used in more than one type of query, multiple column
index types might be appropriate. The following table shows which index types
make good combinations.
Table 4-4: Mix of valid indexes
Note The High_Group index in Adaptive Server IQ Version 12.0 differs from
earlier versions. For some columns you may want both High_Group and
High_Non_Group; previously, it did not make sense to have both.
Adaptive Server IQ index types
This section explores in depth the reasons you might use each of the column
index types.
Add Index
Existing Index HG HNG LF
HG - 1 2
HNG 1 - 1
LF 2 1 -
1 = A reasonable combination
2 = An unlikely combination