Скачать или смотреть Using PostgREST to Query Multiple Conditions from PostgreSQL Tables

Discover how to effectively use `PostgREST` to perform select queries that involve multiple conditions with an `IN` clause in PostgreSQL.
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Handling Multi-Column Queries in PostgREST

When working with databases, it's not uncommon to encounter scenarios where you need to filter results based on multiple conditions. One such example is trying to select rows based on combinations of values from two columns. In this guide, we'll explore how to handle such queries using PostgREST, a powerful tool for interacting with PostgreSQL databases through a RESTful API.

The Problem

Imagine you have a PostgreSQL table named test_1 structured as follows:

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

You want to retrieve all rows where the combination of container_id and product_id is in a specific set of values. For example, you might want to select rows where:

(1, 1)

(1, 2)

(2, 1)

An SQL query to achieve this would look like the following:

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

However, using traditional SQL syntax isn’t directly translatable to PostgREST queries, especially since you might not be able to leverage the IN clause for multiple column comparisons in its API format.

The Solution

As of PostgREST version 10, there is no operator that supports multi-column IN condition directly. However, you can achieve the desired result by using the OR operator in combination with AND. Here’s how you can do it systematically.

Simplifying the Query with OR

Instead of trying to condense the query into a single IN condition, you can break it down to use OR statements. Your SQL equivalent would look like this:

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

Translating to PostgREST Format

You can express the above logic using PostgREST's URL query format. Here’s how the request would look:

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

Explanation of the URL Structure

http://localhost:3000/test_1: This part indicates the resource you are querying (the test_1 table).

?or=: This initiates the query where you wish to filter multiple conditions using an OR clause.

and(...): This part is used within each OR condition to specify that both container_id and product_id must match for each respective condition.

Conclusion

While querying multi-column conditions might initially seem cumbersome with PostgREST, you can effectively use the OR and AND operators to achieve your desired outcomes. The syntax may be more verbose, but it allows for fine-tuned search conditions when accessing your PostgreSQL tables through an API.

By reorganizing how you approach your SQL queries in PostgREST, you can efficiently retrieve the data you need, all while maintaining the flexibility and power of your database. Happy querying!