Move migration filter into delete query

notifier/database/migrations/008-split-post-context.up.sql

@@ -108,69 +108,6 @@ FROM
   category ON category.id = thread.category_id
   LEFT JOIN
   post AS parent_post ON parent_post.id = post.parent_post_id
-WHERE
-  -- Remove would-be-notifiable posts older than 1 year
-  post.posted_timestamp > ((
-    SELECT MAX(posted_timestamp) FROM post
-  ) - (60 * 60 * 24 * 365))
-  -- Select posts for which exists a user config that is going to be notified about it
-  AND EXISTS (
-    SELECT NULL FROM
-      user_config
-    WHERE (
-      -- Filter out users who would already have been notified about this post, regardless of their user config
-      user_config.notified_timestamp < post.posted_timestamp
-      -- Filter out users who are manually unsubscribed to replies to this post's parent OR to this post's thread
-      AND NOT EXISTS (
-        SELECT NULL FROM
-          manual_sub
-        WHERE
-          manual_sub.user_id = user_config.user_id
-          AND manual_sub.thread_id = thread.id
-          AND (
-            manual_sub.post_id = parent_post.id
-            OR manual_sub.post_id IS NULL
-          )
-          AND manual_sub.sub = -1
-      )
-      -- Filter out posts made by the current user
-      AND post.user_id <> user_config.user_id
-      -- Filter out users with chosen frequency outside of defined list, e.g. 'never', who are effectively removed from the service
-      AND user_config.frequency IN (
-        "hourly", "8hourly", "daily", "weekly", "monthly"
-      )
-      -- Filter out posts that the recipient has already responded to, as while the extant query no longer has this filter, it will already have been applied to old posts in the database
-      AND NOT EXISTS (
-        SELECT NULL FROM
-          post AS user_response_child_post
-        WHERE
-          user_response_child_post.user_id = user_config.user_id
-          AND user_response_child_post.parent_post_id = post.id
-      )
-
-      -- Find users who are waiting to be notified about this post
-      AND (
-        -- Find a user who is manually subscribed to replies to this post's parent OR to this post's thread
-        EXISTS (
-          SELECT NULL FROM
-            manual_sub
-          WHERE
-            manual_sub.user_id = user_config.user_id
-            AND manual_sub.thread_id = thread.id
-            AND (
-              manual_sub.post_id = parent_post.id
-              OR manual_sub.post_id IS NULL
-            )
-            AND manual_sub.sub = 1
-        )
-        -- Find a user who is automatically subscribed to the thread
-        OR first_post_in_thread.user_id = user_config.user_id
-        -- Find a user who is automatically subscribed to the post's parent
-        OR parent_post.user_id = user_config.user_id
-      )
-    )
-  );
-
 SELECT "notifiable_post", COUNT(*) FROM notifiable_post;
 
 -- 2. Context tables

notifier/database/queries/delete_non_notifiable_posts.sql

@@ -0,0 +1,69 @@
+-- Purge posts that are no longer considered notifiable
+
+DELETE
+  notifiable_post
+FROM
+  notifiable_post AS post
+
+  INNER JOIN context_thread
+  ON context_thread.thread_id = post.context_thread_id
+
+  LEFT JOIN context_parent_post
+  ON context_parent_post.post_id = post.context_parent_post_id
+WHERE
+  -- Remove posts older than 1 year, no matter what
+  post.posted_timestamp < ((
+    SELECT MAX(posted_timestamp) FROM post
+  ) - (60 * 60 * 24 * 365))
+
+  -- Remove posts for which there exist 0 users who will be notified about it
+  OR NOT EXISTS (
+    -- Attempt to find a user who will be notified by this post
+    SELECT NULL FROM
+      user_config
+
+      LEFT JOIN manual_sub AS thread_sub
+      ON thread_sub.user_id = user_config.user_id
+      AND thread_sub.thread_id = notifiable_post.context_thread_id
+      AND thread_sub.post_id IS NULL
+
+      LEFT JOIN manual_sub AS post_sub
+      ON post_sub.user_id = user_config.user_id
+      AND post_sub.thread_id = notifiable_post.context_thread_id
+      AND post_sub.post_id = notifiable_post.parent_post_id
+
+    WHERE (
+      -- Include only users with chosen frequency in a defined list - other users e.g. those on the 'never' frequency are effectively unsubscribed
+      user_config.frequency IN (
+        "hourly", "8hourly", "daily", "weekly", "monthly"
+      )
+
+      -- Users are not notified about their own posts
+      AND post.author_user_id <> user_config.user_id
+
+      -- Only users last notified before this post was posted
+      AND post.posted_timestamp > user_config.notified_timestamp
+
+      -- Filter out users unsubscribed to this post
+      AND (
+        thread_sub.sub IS NULL OR thread_sub.sub = 1
+        -- Post reply overrides thread unsubscription
+        OR post_sub.sub = 1
+        OR post_with_context.parent_post_user_id = user_config.user_id
+      )
+      AND (post_sub.sub IS NULL OR post_sub.sub = 1)
+    )
+
+      -- Only users subscribed to this post
+      AND (
+        -- Posts in threads started by the user
+        context_thread.first_post_author_user_id = user_config.user_id
+
+        -- Replies to posts made by the user
+        OR context_parent_post.author_user_id = user_config.user_id
+
+        -- Manual subscriptions
+        OR thread_sub.sub = 1
+        OR post_sub.sub = 1
+      )
+  );