Скачать или смотреть How to Combine Two Tables in SQL and Add a New Column

Learn how to effectively combine two tables in SQL while adding a new column for better data organization and analysis.
---
This video is based on the question https://stackoverflow.com/q/64231222/ asked by the user 'Karthick Ramesh' ( https://stackoverflow.com/u/2515456/ ) and on the answer https://stackoverflow.com/a/64231542/ provided by the user 'Thorsten Kettner' ( https://stackoverflow.com/u/2270762/ ) 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: Combining 2 Tables in SQL and add a new column to a Table

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

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Combining Two Tables in SQL and Adding a New Column

In the world of databases, there often arises a need to merge tables for comprehensive data analysis. This guide addresses a common scenario faced by many SQL users: combining two tables and adding a new column based on certain conditions. We'll dive into a specific example involving customer data to demonstrate how this can be accomplished effectively.

The Problem at Hand

Imagine you have two tables in a MySQL database: CustomerDetails and FavoriteCustomers. The structure of these tables is as follows:

CustomerDetails: Contains the columns ID, UUID, Name, Age.

FavoriteCustomers: Contains the columns ID, UUID.

In the CustomerDetails table, the columns ID and UUID together create a unique identifier for each customer. Now, say you want to retrieve a list that includes each customer's ID, UUID, Name, Age, and an indication of whether they are among the favorite customers—all while filtering to only show customers older than 30.

The desired output should look like:

ID

UUID

Name

Age

isFavorite

Key Considerations

Data Volume: The CustomerDetails table may contain a large number of entries (e.g., 10,000 rows), while the FavoriteCustomers table might have relatively few entries.

Combining Logic: To determine if a customer is favorite or not based on the ID and UUID.

The Solution

To accomplish the task of combining the two tables and adding the new column isFavorite, we can utilize a SQL query that incorporates subqueries with the IN clause. Let's break down the solution step by step.

The SQL Query

Here’s the SQL command you would use to achieve the desired results:

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

Breakdown of the SQL Query

SELECT Statement: This part specifies the columns we want to retrieve, which include id, uuid, name, and age from the CustomerDetails table.

is_favorite: It uses the condition (id, uuid) IN (SELECT id, uuid FROM favoritecustomers) to check if the combination of ID and UUID exists in the FavoriteCustomers table. This will return TRUE (or 1) if the customer is a favorite, otherwise FALSE (or 0).

WHERE Clause: The condition WHERE age > 30 filters the results to only include customers who are older than 30 years.

Conclusion

With the SQL query provided, you can effectively combine two tables and add an additional column that checks for favorite status based on specific criteria. This technique not only streamlines your data but also enhances your analytical capabilities by allowing you to filter and display relevant information quickly.

In summary, merging tables in SQL is straightforward when using the right queries and conditions. By employing logical operators, you can create versatile and informative data sets to better understand your business needs.

Next Steps

Feel free to experiment with the above SQL query in your database management system. Tailor the columns and conditions to fit your specific requirements, and watch how your data comes together beautifully!