From 4794a9a6c18439657a2f888d394a85ae93368190 Mon Sep 17 00:00:00 2001
From: Yasuo Honda <yasuo.honda@gmail.com>
Date: Mon, 16 Mar 2015 12:52:02 +0000
Subject: Materialize subqueries by adding `DISTINCT` to support MySQL 5.7.6
`optimizer_switch='derived_merge=on'`
---
.../lib/active_record/connection_adapters/abstract_mysql_adapter.rb | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
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 9625fcf9b8..7e41772227 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -785,7 +785,9 @@ module ActiveRecord
subselect = Arel::SelectManager.new(select.engine)
subselect.project Arel.sql(key.name)
- subselect.from subsubselect.as('__active_record_temp')
+ # Materialized subquery by adding distinct
+ # to work with MySQL 5.7.6 which sets optimizer_switch='derived_merge=on'
+ subselect.from subsubselect.distinct.as('__active_record_temp')
end
def add_index_length(option_strings, column_names, options = {})
--
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