External Entities Database storage

External Entities Database storage (plugin for External Entities) enables the use of external database/schema data into Drupal as external entities. It requires Database Cross-Schema queries module to query multiple databases from a same Drupal instance.

The principle is that it builds your external entity object from an SQL query: the selected columns are your entity field. It is possible to use simple queries as well as really complex queries even with sub-queries or computed values in the SELECT clause.