How to Concatenate Regclass Name with a String in PostgreSQL Query

Learn how to create dynamic SQL in PostgreSQL to concatenate regclass names when creating indexes on partitioned tables.
---
This video is based on the question https://stackoverflow.com/q/65310835/ asked by the user 'user1298426' ( https://stackoverflow.com/u/1298426/ ) and on the answer https://stackoverflow.com/a/65310998/ provided by the user 'Pavel Stehule' ( https://stackoverflow.com/u/406691/ ) 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: How to concat regclass name with a string in postgres query

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.
---
How to Concatenate Regclass Name with a String in PostgreSQL Query

When working with PostgreSQL, especially in complex database schemas involving partitioned tables, engineers often face challenges while trying to execute dynamic SQL queries. One common requirement is the need to concatenate the regclass name (which refers to an OID) with a string for index creation. In this blog, we'll explore how to address this problem effectively by using dynamic SQL in PostgreSQL.

The Challenge

Imagine you have a base partitioned table named test.t and you want to create indexes for its partitioned tables. During this process, you may run into the following error when trying to concatenate a regclass name with a string for an index name:

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

This error arises because DDL (Data Definition Language) statements do not support parameterization in PostgreSQL. This means you cannot directly use variables within the CREATE INDEX statement. So how can we resolve this issue? Let's dig deeper into an elegant solution using dynamic SQL.

The Solution: Dynamic SQL with EXECUTE

To successfully create indexes with concatenated names, we will use the EXECUTE statement in PostgreSQL. Here’s a simplified breakdown of the steps involved in the solution:

Step 1: Define the Function

You need to create a PL/pgSQL function that will iterate through all partition tables and create an index for each one.

Step 2: Use a Loop to Fetch Partition Tables

Utilize a cursor to select all partitioned tables associated with the parent table test.t. This can be achieved using the pg_catalog.pg_inherits table and joining it with the pg_class table to get the names of the partitions.

Step 3: Construct the Dynamic SQL

Inside the loop that fetches the partition table names, use the EXECUTE FORMAT function to construct the dynamic SQL. This allows you to concatenate the desired strings with variables dynamically.

Example Code

Here is an example of how your function might look after implementing the solution:

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

Conclusion

By harnessing the power of dynamic SQL and the EXECUTE statement, you can effectively overcome the limitations of DDL statements in PostgreSQL. This allows for flexibility and efficiency in managing partitioned tables, ensuring that index creation can be performed dynamically based on the existing structure of your database.

Try implementing this approach in your PostgreSQL projects to streamline your database operations, especially when working with partitioned tables. Happy querying!