Sybase IQ indexes are optimized according to the number of unique (distinct) values they include. When this number reaches certain levels, choose indexes according to the recommendations in Table 6-2.
Number of Unique Values |
Recommended Index Type |
|---|---|
Below 1,000 |
LF (HG if table has <25,000 rows) |
1000 and over |
HG and/or HNG |
Columns created when MINIMIZE_STORAGE option
is ON, or for which you specify IQ UNIQUE 65536 or
less, are automatically placed in a form of the default index that
is optimized for reduced storage, and improved performance for certain
types of queries.
Here are some examples of columns with different numbers of unique values:
Columns that hold marital status have just a few unique values (single, married, NULL)
Columns that hold state or province names have fewer than 100 unique values
Columns that hold date data probably have more than 100 but fewer than 65536 unique values
Columns that hold account numbers or social security numbers may have thousands or millions of unique numbers
