However, we want just the top two from each group. Once you’ve built your window, you’re ready for the window function: rank() returns the position of the record within its group or window. ORDER BY within an OVER clause tells PostgreSQL how to order each group. In this case, it builds groups of the same color. PARTITION BY splits, or partitions, the data into groups with the same value for the specified column. OVER describes how to window the results. The most interesting piece is the inner query that utilizes the OVER clause. Let’s break down what’s going on in each piece. We can use that to add a column to our result set that represents the rank of each item in its respective group. Window functions are similar to aggregate functions, but instead of operating on groups of records to produce a single output record, they operate on records related to the current row. My project was being built on PostgreSQL, so I turned to my handy dandy window functions. I wanted to select the top two items, grouped by color, and sorted by when they were created. For a recent project, I found myself needing to get certain data out of our database.
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