Скачать или смотреть How to List All UNIQUE Constraints in a Specific PostgreSQL Schema

Discover how to effectively list all `UNIQUE` constraints in a PostgreSQL schema with a clean and organized query. Get expected results and improve your database management skills.
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This video is based on the question https://stackoverflow.com/q/74114593/ asked by the user 'ca5p3r' ( https://stackoverflow.com/u/9851488/ ) and on the answer https://stackoverflow.com/a/74114947/ provided by the user 'Laurenz Albe' ( https://stackoverflow.com/u/6464308/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Listing All UNIQUE Constraints in a PostgreSQL Schema

In PostgreSQL, ensuring that certain columns in your tables have unique values is a common requirement. That's where UNIQUE constraints come into play. If you're working with a specific schema and need to list all UNIQUE constraints, you might run into some challenges with the default query results. In this guide, we will explain how to get a clear and organized display of these constraints.

The Problem: Unclear Results from Default Queries

When trying to list UNIQUE constraints, users often rely on a standard SQL query. For example, one might use the following query to fetch the constraints information:

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

However, as seen in the example with the myTable, this query tends to create multiple repetitive rows for each column involved in the UNIQUE constraint, making the output cluttered and hard to understand.

Sample Output Issues

Given the following table definition:

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

The output can be likened to the following messy result:

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

The Solution: A Cleaner Query

To address these cluttered results, you can modify your approach. Instead of relying on the information_schema, you can utilize PostgreSQL’s metadata directly to obtain a cleaner, more organized output that groups the columns involved in each UNIQUE constraint.

Enhanced Query

Here’s an optimized version of the SQL query you can use:

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

Explaining the Query

Table Relations:

pg_constraint holds information about constraints, including unique constraints.

Using CROSS JOIN LATERAL, you can expand the array of columns (conkey) that each constraint pertains to.

Grouping and Aggregating:

The array_agg function aggregates the column names involved in the UNIQUE constraint, grouped by each constraint’s unique identifier.

Filtering for the Schema:

Make sure to specify your own schema by replacing 'mySchema' in the WHERE clause.

Expected Output

When executed, the above query should yield a neat result:

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

This result clearly groups the columns associated with the UNIQUE constraint, giving you a better representation of your data structure.

Conclusion

Listing all UNIQUE constraints effectively helps maintain data integrity within your databases. By adopting a cleaner query method, you can improve your database management practices significantly. Use the provided query to enhance your schema inspection process and keep your database organized.

Feel free to reach out in the comments if you have any questions or if you need further assistance with PostgreSQL queries!