Cardinality values can be derived from an approximate quantile summary. An approximate quantile summary can be generated for a column of a database table at data ingestion, data update, upon request, in response to a query, and in various other scenarios. When a query is received that includes a predicate directed to the column of the approximate quantile summary, a cardinality value may be derived from the boundary values of one or more quantiles that include the predicate. The cardinality value may then be used to select a query plan. The query may be performed according to the selected query plan.