Join logic is central to financial and operational reporting because analysts often combine claim, member, provider, and payment data from multiple tables. Choosing the wrong join can silently drop rows or create duplicates, which can distort results in Providence reporting workflows.
Explain the main types of SQL joins and when you would use each: INNER JOIN, LEFT JOIN, RIGHT JOIN, FULL OUTER JOIN, CROSS JOIN, and SELF JOIN. As part of your answer, describe what rows each join returns, how unmatched rows appear, and how NULL values affect interpretation.
You should answer at an interview level: define each join clearly, compare them, and give a practical example of when an analyst would choose one over another in a finance or healthcare reporting context. You do not need to discuss optimizer internals, but you should mention common mistakes such as filtering a LEFT JOIN in the WHERE clause and accidentally turning it into an INNER JOIN.