The set of indexes you define for any given column can have dramatic impact on the speed of query processing. There are four main criteria for choosing indexes:
Number of unique values
Types of queries
Disk space usage
Data types
Use the recommendations for all criteria in combination, rather than individually. Remember also that all columns are automatically stored in a way that facilitates fast projections. To decide on additional indexes, look closely at the data in each column. Try to anticipate the number of unique and total values, the query results users want from it, and whether the data is used in ad hoc joins or join indexes.
For details of index types, and criteria to use for choosing the correct types, see the sections that follow.
