Low_Fast (LF) Index

This index is ideal for columns that have a very low number of unique values (under 1,000) such as sex, Yes/No, True/False, number of dependents, wage class, and so on. LF is the fastest index in SAP Sybase IQ.

When you test for equality, just one lookup quickly gives the result set. To test for inequality, you may need to examine a few more lookups. Calculations such as SUM, AVG, and COUNT are also very fast with this index.

As the number of unique values in a column increases, performance starts to degrade and memory and disk requirements start to increase for insertions and some queries. When doing equality tests, though, it is still the fastest index, even for columns with many unique values.

• Recommended Use
  Use an LF index when a column has fewer than 1,000 unique values, or a column has fewer than 1,000 unique values and is used in a join predicate.
• Advantages and Disadvantages of Low_Fast
  Low_Fast indexes have advantages and disadvantages.
• Comparison with Other Indexes
  Familiarize yourself with how the LF index compares to other indexes.
• Additional Indexes
  The High_Non_Group index type may be appropriate for a Low_Fast column.