Theinner joinoperation retrievesonly the records that exist in both tables, which is theintersectionof two datasets.
In clinical data management, relational databases often store related data in multiple tables—for example, demographic data in one table and lab results in another. When a Data Manager needs to extract records that exist in both (e.g., subjects appearing in both demographics and labs), aninner joinis used.
According to theGCDMP (Chapter: Database Design and Build), joins are fundamental relational operations ensuring data consistency and integrity across multiple data domains.
Inner join:Returns matching records from both tables (intersection).
Left/right outer joins:Return all records from one table and matching records from the other (preserving nonmatches).
Full outer join:Returns all records from both tables, whether matched or not.
Therefore, to select only the50 records commonto both tables, the correct operation is aninner join.
Reference (CCDM-Verified Sources):
SCDM Good Clinical Data Management Practices (GCDMP), Chapter: Database Design and Build, Section 4.3 – Relational Database Concepts and Joins
ICH E6 (R2) Good Clinical Practice, Section 5.5.3 – Data Processing and Validation
