Which statement about external data sources in Salesforce is true?

The statement about external data sources in Salesforce that is true is that they allow real-time access without storing data in Salesforce. This feature is a key aspect of Salesforce's integration capabilities, enabling users to access and interact with data that resides in external systems without the need to replicate or store that data within Salesforce itself.

This real-time access is particularly beneficial for organizations that rely on large datasets that they do not want to duplicate in Salesforce due to storage constraints or the desire for data integrity. By using Salesforce Connect and external objects, users can view and edit data stored in external systems through the Salesforce interface, all while keeping the data live and up-to-date.

The other options are not accurate representations of how external data sources function within Salesforce. They do not always store data within Salesforce; instead, they provide a way to link to that data externally. Access is not limited to custom code, as Salesforce provides declarative tools that allow users to create and manage external data sources without needing to write code. Finally, external data sources are not restricted to only SQL-based queries; they can support a variety of query types depending on the integration method.