Add uniqTheta Aggregate Function for Theta Sketch in ClickHouse

Why it matters

The uniqTheta function integrates the Theta Sketch algorithm into ClickHouse, allowing users to efficiently estimate the cardinality of large datasets with high accuracy and low memory usage. This helps solve the problem of computing approximate distinct counts at scale, improving performance and resource utilization.

How to use it

Users can apply the new aggregate function uniqTheta in their SQL queries to perform approximate distinct counts using Theta Sketch. For example:

SELECT uniqTheta(column_name) FROM table_name;

This will return the approximate number of unique values in column_name using the Theta Sketch algorithm.