Скачать или смотреть Retrieving Latest Data from Today and Yesterday in PostgreSQL

Learn how to easily get today's and yesterday's latest records from your time-series data using PostgreSQL's built-in functions.
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Retrieving Latest Data from Today and Yesterday in PostgreSQL

If you work with time-series data in PostgreSQL, you might often find yourself needing to extract the most recent records from specific time frames. This is a common requirement especially in analytical contexts where knowing the latest values is crucial for decision-making. In this guide, we’ll tackle a common problem: how to retrieve today’s and yesterday’s latest records from your dataset.

Understanding the Problem

Let’s consider an example scenario. You have a table that consists of time-series data including records of prices, amounts, average ratings, and timestamps. After inspecting your records, you realize you need to pull just the latest entry for both today and yesterday.

Sample Data

For our example, here’s a snippet of the data we're working with:

[[See Video to Reveal this Text or Code Snippet]]

From the above data, we want to extract the latest records for both today and yesterday like this:

[[See Video to Reveal this Text or Code Snippet]]

The Solution

To solve this problem efficiently, we will employ PostgreSQL's ROW_NUMBER() function along with partitioning capabilities to get the latest entry for our specified dates. Here’s how:

Steps to Retrieve the Latest Records

Extract the Date: We will extract the date part of the time column since we want to group by date.

Use the ROW_NUMBER() Function: This function will allow us to rank entries within each partition (which is our date here) based on the time in descending order.

Filter Based on Current Date: We'll ensure that we're only looking at data for today and yesterday using current_date.

The Complete Query

Here’s the SQL query you would execute:

[[See Video to Reveal this Text or Code Snippet]]

Breakdown of the Query

PARTITION BY: This clause segments the data into groups based on the extracted date.

ORDER BY time DESC: This ensures we are looking at the most recent data first.

ROW_NUMBER(): This function assigns a unique number to each row within the partition, starting at 1 for the latest entry.

**Filtering with WHERE: The outer query selects only the first row (latest entry) from each date group.

Conclusion

Retrieving today’s and yesterday’s latest records in PostgreSQL can be accomplished effortlessly with the right use of SQL functions. By leveraging ROW_NUMBER() and the appropriate date filtering, you can ensure you're getting the most relevant and recent data for your analysis.

Have any questions or need further assistance with PostgreSQL? Feel free to leave your thoughts in the comments below!