Скачать или смотреть How to Use SELECT in a RETURNING Statement in PostgreSQL

Discover how to include a `SELECT` statement in a `RETURNING` clause for your PostgreSQL queries, enhancing your database operations.
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Unlocking the Power of PostgreSQL: Including SELECT in RETURNING Statements

When working with PostgreSQL, you may encounter situations where you want to retrieve additional information after performing an INSERT operation. A common question developers ask is whether it's possible to include a SELECT statement within a RETURNING clause. Today, we're diving into that problem and exploring the correct syntax to achieve it.

The Challenge

Let's say you have an INSERT statement that adds a new record into a table, such as user_skills_languages. You may want to retrieve the IDs of the inserted records, along with some related information, such as the name of a skill from another table. The goal is to both insert data and get back relevant details in one go.

Here's a snippet of what someone might try:

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

However, as you’ve probably guessed, this syntax won’t execute as expected. So, how can you successfully incorporate a SELECT clause into a RETURNING statement?

The Solution

Yes, it's certainly possible! The trick lies in enclosing the subquery in parentheses. Here is how to correctly implement this:

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

Breaking Down the Solution

Basic Structure: The RETURNING clause in PostgreSQL allows you to retrieve values from the inserted rows. However, to include a query that retrieves additional data, it must be formatted correctly.

Subquery Usage: A subquery is a query nested inside another SQL query. By placing your SELECT within parentheses, PostgreSQL treats it as a manageable component of the RETURNING clause.

Understanding the Context: The modified statement achieves both goals: inserting a new record into user_skills_languages and obtaining:

skill_id: the ID of the inserted skill.

skill_type_id: the type associated with that skill.

name: the name of the skill from the skills table.

Important Considerations

Ensure Validity: Make sure that your subquery returns only one value. If your SELECT statement could return multiple rows, PostgreSQL will throw an error.

Performance: Incorporating subqueries can affect performance, especially if the SELECT statement is complex or if it accesses a large dataset. Always examine your execution plans when optimizing.

Conclusion

With the correct syntax, incorporating a SELECT within a RETURNING clause can simplify your data manipulation tasks and enhance your query's functionality. This technique is invaluable for developers who need to retrieve and return multiple pieces of data from their database transactions in a single query.

So next time you write an INSERT statement in PostgreSQL, don't forget that you can gather additional information seamlessly with the proper syntax!