https://nalar.dev/tags/subqueries/ Recent content in Subqueries on Nalar Hugo en-us Fri, 04 Sep 2026 00:00:00 +0700 https://nalar.dev/use-exists-and-not-exists-for-relationship-checks-in-sql/ Fri, 04 Sep 2026 00:00:00 +0700 https://nalar.dev/use-exists-and-not-exists-for-relationship-checks-in-sql/ <p>Many SQL queries do not actually need data from a related table. They only need to answer a yes-or-no question:</p> <ul> <li>Does this customer have at least one paid order?</li> <li>Is this project missing an active owner?</li> <li>Does any inventory row satisfy this product requirement?</li> </ul> <p>A common first attempt is to join the tables and then remove duplicates. That can work, but it makes the query produce more rows than the problem requires and then asks a later operation to repair the result.</p>