From fcfce3e426a64ffa567c572eeeaeb2ef700b15dc Mon Sep 17 00:00:00 2001
From: Sam <sam.saffron@gmail.com>
Date: Mon, 15 Jan 2018 16:38:58 +1100
Subject: [PATCH] PERF: avoid expensive OR clause query info more efficiently

---
 lib/topic_query.rb | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/lib/topic_query.rb b/lib/topic_query.rb
index 3dae7132e09..2d27044739b 100644
--- a/lib/topic_query.rb
+++ b/lib/topic_query.rb
@@ -512,7 +512,17 @@ class TopicQuery
         if options[:no_subcategories]
           result = result.where('categories.id = ?', category_id)
         else
-          result = result.where('categories.id = :category_id OR (categories.parent_category_id = :category_id AND categories.topic_id <> topics.id)', category_id: category_id)
+          sql = <<~SQL
+            categories.id IN (
+              SELECT c2.id FROM categories c2 WHERE c2.parent_category_id = :category_id
+              UNION ALL
+              SELECT :category_id
+            ) AND
+            topics.id NOT IN (
+              SELECT c3.topic_id FROM categories c3 WHERE c3.parent_category_id = :category_id
+            )
+          SQL
+          result = result.where(sql, category_id: category_id)
         end
         result = result.references(:categories)