Avoid calling `current_database` in `table_comment`

`current_database` executes a query and `table_comment` is called to all
tables even if a table does not have a comment. Using `current_database`
increases extra queries.

1 files changed, 4 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 01395d8ceb..c73159b796 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -410,11 +410,13 @@ module ActiveRecord
       end
 
       def table_comment(table_name) # :nodoc:
+        schema, name = extract_schema_qualified_name(table_name)
+
         select_value(<<-SQL.strip_heredoc, 'SCHEMA')
           SELECT table_comment
           FROM information_schema.tables
-          WHERE table_schema=#{quote(current_database)}
-            AND table_name=#{quote(table_name)}
+          WHERE table_schema = #{quote(schema)}
+            AND table_name = #{quote(name)}
         SQL
       end