SQL Joins in PostgreSQL: Patients, Doctors, and the Rows That Go Missing

SQL joins enable combining rows from multiple tables using related columns. In PostgreSQL, this prevents data redundancy by separating entities like patients and appointments. Different join types handle unmatched rows differently: Inner Join returns only records with matching values in both tables, while Left Outer Join retrieves all left table records and matching right records, filling gaps with NULL. Choosing the incorrect join can cause rows to disappear from results without warning, requiring careful selection based on function.