Intro

When optimizing database queries, one crucial factor is estimating the Number of Distinct Values (NDV) after operations like filtering or sampling. Let’s explore how this works in a practical way. What is NDV? NDV (Number of Distinct Values) counts how many unique values exist in a dataset. For instance, in a table with 1000 customer records, a “country” column might have only 50 distinct values since many customers are from the same countries. ...