How to Efficiently Create Comma-Separated Lists from Relational Database Tables using SQL?

Efficiently Creating Comma-Separated Lists Using SQL

Database tasks frequently require concatenating data fields into comma-separated lists. SQL offers efficient solutions, eliminating the need for procedural code.

Example: Imagine three tables: Applications (id, name), Resources (id, name), and ApplicationsResources (id, app_id, resource_id). The objective is to generate a report showing each resource name alongside a comma-separated list of associated applications.

This can be achieved using GROUP_CONCAT (MySQL and some SQL Server versions) or STRING_AGG (SQL Server 2017 and later). These functions efficiently concatenate values grouped by a specific column.

MySQL/Some SQL Server Versions:

SELECT r.name, GROUP_CONCAT(a.name SEPARATOR ',') AS application_names
FROM RESOURCES r
JOIN APPLICATIONSRESOURCES ar ON ar.resource_id = r.id
JOIN APPLICATIONS a ON a.id = ar.app_id
GROUP BY r.name;

SQL Server 2017 and Later:

SELECT r.name, STRING_AGG(a.name, ',') AS application_names
FROM RESOURCES r
JOIN APPLICATIONSRESOURCES ar ON ar.resource_id = r.id
JOIN APPLICATIONS a ON a.id = ar.app_id
GROUP BY r.name;

Oracle:

Oracle offers several string aggregation methods, including LISTAGG and the DBMS_PCL_ROWPKT package. Consult Oracle documentation for detailed instructions.

This SQL-based approach offers a streamlined method for generating comma-separated lists, directly within your database queries, improving data presentation in applications and GUIs.

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