The inner join operation retrieves only the records that exist in both tables, which is the intersection of 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), an inner join is used.
According to the GCDMP (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 the 50 records common to both tables, the correct operation is an inner 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