*Real life:* A questionnaire is grouped into several sections (e.g. personal details, contacts, education, work experience etc), each section then has multiple questions. *Current implementation:* I have 3 tables; questionnaires (columns: id, title, ...), sections (id, questionnaire_id, ...) and questions (id, section_id, ...). The columns questionnaire_id and section_id are indexed, and all "id" columns are primary keys, auto increment. *The need:* I need to get all questions that belong to a specific questionnaire. Lets assume the id of this questionnaire is 1. *Method 1:* 1. Run the query "SELECT id FROM sections WHERE questionnaire_id=1" 2. Do some PHP code to retrieve the ids and convert them into CSV format, e.g. 1, 2, 3 3. Run the query "SELECT id, title, ... FROM questions WHERE section_id IN (1,2,3)" *Method 2:* 1. Run the query "SELECT id, title, ... FROM questions WHERE section_id IN (SELECT id FROM sections WHERE questionnaire_id=1)" *Question:* Which is the better method in terms of speed and scalability?