SQL Essentials: KEEP Function Explained

Overview

The KEEP() function in SQL is used in conjunction with aggregate functions to return specific values from a group of rows based on a defined ordering. In simpler terms, it allows you to extract a particular value (such as the first or last entry) within a grouped dataset, according to a specified sort order. This is particularly useful when you need to retrieve the most recent or earliest record in a set, like identifying the latest transaction for each customer.

Understanding the Syntax

The general syntax for using the KEEP() function with an aggregate function is:

AGGREGATE_FUNCTION(column_name) KEEP (DENSE_RANK FIRST | LAST ORDER BY column_name)