This lecture introduces conditional queries in the context of geographic information systems, covering the syntax of conditional queries, understanding how joins work, and the use of WHERE clause for filtering data. The lecture also explains operators like IN, BETWEEN, IS NULL, and LIKE, and how to combine conditions using AND and OR. It delves into different types of joins, such as INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN, to combine information from multiple tables based on common fields.