Скачать или смотреть Efficiently Insert Rows Based on User Ticket Assignments in PostgreSQL

Learn how to dynamically insert multiple rows into your PostgreSQL tickets table using a seamless SQL query with `generate_series` and an `INNER JOIN`.
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This video is based on the question https://stackoverflow.com/q/69408478/ asked by the user 'Ana Cruz' ( https://stackoverflow.com/u/16235935/ ) and on the answer https://stackoverflow.com/a/69408959/ provided by the user 'Anton Grig' ( https://stackoverflow.com/u/11769859/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Insert Multiple Rows in PostgreSQL Based on Another Table's Values

Managing user assignments in a ticketing system can be challenging, especially when trying to populate tables dynamically based on user input. For example, let's say you have a users table containing user data along with a specified quantity of tickets assigned to each user. How can you efficiently generate the entries needed in a tickets table without manually inserting each row? In this guide, we'll explore how to automate this process in PostgreSQL.

Problem Overview

Consider the following structure of two tables:

Users Table:

User_idNameQuantity1Ana32Mark4From this data, you want to create a tickets table that includes an entry for each assigned ticket, linking back to the respective user. The desired tickets table should appear as follows:

Tickets Table:

Ticket_idUser_id11213142526272The challenge is to insert all these entries without tedious manual addition. Let’s dive into a solution.

Solution: Using INNER JOIN and generate_series

To efficiently populate the tickets table based on the users table, we can leverage PostgreSQL's built-in functions. Specifically, the generate_series() function helps us create a series of numbers dynamically, which corresponds to the ticket quantity for each user.

Step-by-Step SQL Query

The following query accomplishes this task:

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

Explanation of the Query Components:

INSERT INTO Tickets (user_id):

This portion specifies that we are inserting values into the user_id field of the tickets table.

SELECT user_id:

We are selecting the user_id from the users table to indicate which users will be associated with the new tickets.

FROM Users:

Indicates that we are pulling data from the users table.

INNER JOIN LATERAL generate_series(1, Quantity):

The generate_series(1, Quantity) function generates a list of integers from 1 up to the number specified in the Quantity column.

The LATERAL keyword allows us to reference each row of the users table as it processes the quantities.

ON true:

This condition returns rows for all users and their respective ticket counts, allowing for the cross-join logic to function smoothly.

ORDER BY user_id:

Finally, ordering the results by user_id helps keep the data organized.

Conclusion

Using the above SQL query, you can effortlessly populate the tickets table based on the ticket quantities defined in the users table. This method saves time and reduces the likelihood of human error when manually entering data. By utilizing PostgreSQL's powerful generate_series function along with INNER JOIN LATERAL, you create a flexible and efficient solution for managing users and their ticket assignments.

For further inquiries or enhancements to this implementation, feel free to reach out in the comments below, and happy querying!