Sybase IQ indexes are optimized according to the number of unique (distinct) values they include.
When the number of distinct values reaches certain levels, choose indexes according to the recommendations in this table.
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.
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