Replace dots with an underscore when creating an alias for the CTE

When the Arel table to use as the alias contains a schema in your
name, e.g., "gitlab_secondary"."namespaces" it produces an invalid
query.

lib/gitlab/sql/recursive_cte.rb

@@ -48,7 +48,7 @@ module Gitlab
       #
       # alias_table - The Arel table to use as the alias.
       def alias_to(alias_table)
-        Arel::Nodes::As.new(table, alias_table)
+        Arel::Nodes::As.new(table, Arel::Table.new(alias_table.name.tr('.', '_')))
       end
 
       # Applies the CTE to the given relation, returning a new one that will

spec/lib/gitlab/sql/recursive_cte_spec.rb

@@ -31,6 +31,15 @@ describe Gitlab::SQL::RecursiveCTE, :postgresql do
 
       expect(cte.alias_to(table).to_sql).to eq("#{source_name} AS #{alias_name}")
     end
+
+    it 'replaces dots with an underscore' do
+      table = Arel::Table.new('gitlab.kittens')
+
+      source_name = ActiveRecord::Base.connection.quote_table_name(:cte_name)
+      alias_name = ActiveRecord::Base.connection.quote_table_name(:gitlab_kittens)
+
+      expect(cte.alias_to(table).to_sql).to eq("#{source_name} AS #{alias_name}")
+    end
   end
 
   describe '#apply_to' do