How to Use SQL UNION to Group Rows Effectively

Learn how to achieve an effective SQL query that groups rows using `UNION` and `GROUP BY`. Find out how to combine and aggregate data in your database efficiently.
---
This video is based on the question https://stackoverflow.com/q/66482796/ asked by the user 'canpoint' ( https://stackoverflow.com/u/2409047/ ) and on the answer https://stackoverflow.com/a/66482907/ provided by the user 'eshirvana' ( https://stackoverflow.com/u/1367454/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: SQL union grouped by rows

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/licensing
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/by-sa/4.0/ ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/by-sa/4.0/ ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Use SQL UNION to Group Rows Effectively

When working with SQL databases, it is common to encounter scenarios where you have data spread across multiple rows that need to be consolidated into a single row. In this guide, we’ll explore how to use the SQL UNION statement effectively to group rows based on a common identifier and aggregate other columns into a desired format. Let’s dive in!

The Problem: Combining Rows

Imagine you have a table that contains repeated identifiers with different related data spread over several columns. For instance, consider a table structured like this:

col1col2col3col4commonrowonetwonullcommonrownullnullthreeIn the above table, we have repeated entries for col1 (in this case, "commonrow") with varying values in col2, col3, and col4. Our goal is to consolidate these rows into a single row that captures the maximum value across each column for a given identifier, which would look like this:

col1col2col3col4commonrowonetwothreeThe Solution: SQL Query Breakdown

To achieve the desired result, we can utilize the GROUP BY clause in combination with aggregate functions. Here’s a step-by-step breakdown of how to construct the SQL query:

Step 1: Identify the Columns to Aggregate

In our table, we want to consolidate data from col2, col3, and col4. In SQL, we can use the MAX() function to select the highest value for each of these columns from the grouped rows.

Step 2: Write the SQL Query

Here’s how you can write the SQL query to achieve the desired outcome:

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

Replace your_table_name with the name of your actual table.

Step 3: Executing the Query

Once you execute the above query in your SQL editor, it will aggregate the rows based on col1, fetching the maximum values from the other columns. As a result, you will receive a single row output like the one we wanted:

col1col2col3col4commonrowonetwothreeConclusion

By using the GROUP BY clause in conjunction with the MAX() function, you can effectively aggregate multiple rows in your SQL database into single rows that display the necessary information in a clean format. This approach not only helps in reducing data redundancy but also enhances readability and analysis efficiency.

Now that you understand how to use SQL to combine rows effectively, you can manipulate your data more efficiently in your own databases. Happy querying!

Видео How to Use SQL UNION to Group Rows Effectively канала vlogize