Fix #4951: chartags:0 returning posts with chartags.

* Add fix script to fix posts with incorrect tag_count_* fields.
* Simplify the code for updating tag_count_* fields (no functional change).

script/fixes/088_fix_post_tag_category_counts.rb

@@ -0,0 +1,44 @@
+#!/usr/bin/env ruby
+
+require_relative "base"
+
+with_confirmation do
+  # Fix posts that have a tag_count_* column inconsistent with the true count.
+  posts = Post.find_by_sql(<<~SQL.squish)
+    UPDATE posts
+    SET
+      tag_count_general = true_tag_count_general,
+      tag_count_artist = true_tag_count_artist,
+      tag_count_copyright = true_tag_count_copyright,
+      tag_count_character = true_tag_count_character,
+      tag_count_meta = true_tag_count_meta,
+      tag_count = true_tag_count
+    FROM (
+      SELECT
+        posts.id AS post_id,
+        COUNT(*) FILTER (WHERE category = 0) AS true_tag_count_general,
+        COUNT(*) FILTER (WHERE category = 1) AS true_tag_count_artist,
+        COUNT(*) FILTER (WHERE category = 3) AS true_tag_count_copyright,
+        COUNT(*) FILTER (WHERE category = 4) AS true_tag_count_character,
+        COUNT(*) FILTER (WHERE category = 5) AS true_tag_count_meta,
+        COUNT(*) AS true_tag_count
+      FROM
+        posts,
+        unnest(string_to_array(tag_string, ' ')) tag
+      JOIN tags ON tags.name = tag
+      GROUP BY posts.id
+    ) tag_category_counts
+    WHERE
+      posts.id = tag_category_counts.post_id AND (
+        posts.tag_count_general   != tag_category_counts.true_tag_count_general OR
+        posts.tag_count_artist    != tag_category_counts.true_tag_count_artist OR
+        posts.tag_count_copyright != tag_category_counts.true_tag_count_copyright OR
+        posts.tag_count_character != tag_category_counts.true_tag_count_character OR
+        posts.tag_count_meta      != tag_category_counts.true_tag_count_meta OR
+        posts.tag_count           != tag_category_counts.true_tag_count
+      )
+    RETURNING posts.*
+  SQL
+
+  puts "Fixing #{posts.size} records"
+end