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POSQL sort records based on condition in many to many relation
 

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    <p>I am unable to write SQL to sort records based on condition in many to many relationship. I have table structure <code>tasks</code> with many to many table for task dependencies. E.g. Task C can have one or many dependencies on other tasks trough table <code>task_dependencies</code>. </p> <ul> <li>TASKS: id, user_id, status_id, date_due, ...</li> <li>TASK_DEPENDENCIES: task_id, dependency_task_id (pivot table)</li> <li>Statuses are following: Q-new, G-In progress, L-closed</li> </ul> <p>The idea with task dependencies is that one task can not be started until all his dependency task(s) are closed. I would like to select all user's open tasks. This is easy. But I need to sort them by date_due, but having all the task with dependencies that can not be started yet on the end of result set. Meaning I need to somehow check if all dependency tasks are closed and take this into account when sorting somehow?</p> <p>I managed to put together one select but this always puts all tasks with dependencies at the end of the record set. But I would like to put tasks with closed dependencies in normal date_due order flow... </p> <pre><code>SELECT T.id, T.description, TD.dependency_task_id, ISNULL(TD.dependency_task_id) AS NoDependency, T.date_due FROM tasks T LEFT OUTER JOIN task_dependencies TD ON T.id = TD.task_id WHERE assigned_user_id=1 ORDER BY NoDependency DESC, T.date_due </code></pre> <p>Here is the SQL fiddle: <a href="http://sqlfiddle.com/#!2/894f7/3" rel="nofollow">http://sqlfiddle.com/#!2/894f7/3</a>.</p>
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