Trino supports statistics based optimizations for queries. For a query to take advantage of these optimizations, Trino must have statistical information for the tables in that query.
Table statistics are provided to the query planner by connectors.
The following statistics are available in Trino:
For a table:
row count: the total number of rows in the table
For each column in a table:
data size: the size of the data that needs to be read
nulls fraction: the fraction of null values
distinct value count: the number of distinct values
low value: the smallest value in the column
high value: the largest value in the column
The set of statistics available for a particular query depends on the connector being used and can also vary by table. For example, the Hive connector does not currently provide statistics on data size.
Table statistics can be displayed via the Trino SQL interface using the SHOW STATS command. For the Hive connector, refer to the Hive connector documentation to learn how to update table statistics.