What is a source‑target join, and how would you implement it?

A source‑target join is a data integration technique used to combine data from a source system with a target system, often during data migration or replication. The source contains the original data, while the target is the destination database or data warehouse. In a source‑target join, you typically align records based on a key, such as a primary key or business identifier, and then merge or transform the data to fit the target schema. For example, when migrating customer data from an on‑premises CRM to a cloud‑based data warehouse, you would join the source customer table with the target staging table on the customer ID, then apply transformations like field mapping, data type conversion, and enrichment. This approach ensures data consistency, allows incremental loads, and supports change data capture (CDC). In practice, you might use SQL join statements, ETL tools like Informatica or Talend, or custom scripts in Python or Spark to perform the source‑target join, depending on the volume and complexity of the data.