fix(Dr. Rai Report): Titration Query Updater (#5699)

**Story card:**
[sc-16748](https://app.shortcut.com/simpledotorg/story/16748/fix-titrationdata-populator)

## Because

The original implementation assumed a more recent version of PostgreSQL.
What we use in Simple is still behind

## This addresses

Changing the SQL syntax to match the version of PostgreSQL used in
Simple

## Test instructions

run the rake task

Author: igbanam

app/queries/dr_rai/titration_query_factory.rb

@@ -1,48 +1,28 @@
 module DrRai
   class TitrationQueryFactory < QueryFactory
-    def inserter
-      base_query do
-        "insert into public.dr_rai_data_titrations (month_date, facility_name, follow_up_count, titrated_count, titration_rate)"
-      end
-    end
+    INSERTER_SQL = "insert into public.dr_rai_data_titrations (month_date, facility_name, follow_up_count, titrated_count, titration_rate)".freeze
 
-    def updater
-      <<-SQL
-      merge into public.dr_rai_data_titrations as existing
-      using (#{base_query { "" }}) as incoming
-      on existing.month_date = incoming.month_date and existing.facility_name = incoming.facility_name
-      when not matched
-        insert (
-          month_date,
-          facility_name,
-          follow_up_count,
-          titrated_count,
-          titration_rate,
-          created_at,
-          updated_at
-        )
-        values (
-          incoming.month_date,
-          incoming.facility_name,
-          incoming.follow_up_count,
-          incoming.titrated_count,
-          incoming.titration_rate,
-          now(), -- for created_at
-          now(), -- for updated_at
-        )
-      when matched and existing.titration_rate != incoming.titration_rate
+    CONFLICT_HANDLER_SQL = <<~SQL
+      on conflict (month_date, facility_name) do
         update
           set
-            follow_up_count = incoming.follow_up_count,
-            titrated_count = incoming.titrated_count,
-            titration_rate = incoming.titration_rate,
+            follow_up_count = excluded.follow_up_count,
+            titrated_count = excluded.titrated_count,
+            titration_rate = excluded.titration_rate,
             updated_at = now(); -- ...for good bookkeeping
-      SQL
+    SQL
+
+    def inserter
+      base_query(INSERTER_SQL, "") { |enhancement| enhancement }
+    end
+
+    def updater
+      base_query(INSERTER_SQL, CONFLICT_HANDLER_SQL) { |enhancement| enhancement }
     end
 
     private
 
-    def base_query
+    def base_query inserter, conflict_handler
       <<~SQL
         with facility_titrations as (
           select
@@ -88,12 +68,13 @@ def base_query
           group by month_date
         )
 
-        #{yield}
+        #{yield inserter}
         (
           select * from selected_facility_titrations
           union all
           select * from averages
-        );
+        )
+        #{yield conflict_handler};
       SQL
     end
   end

db/migrate/20250923223358_add_index_to_dr_rai_data_titrations.rb

@@ -0,0 +1,5 @@
+class AddIndexToDrRaiDataTitrations < ActiveRecord::Migration[6.1]
+  def change
+    add_index :dr_rai_data_titrations, [:month_date, :facility_name], unique: true
+  end
+end

db/structure.sql

@@ -7081,6 +7081,13 @@ CREATE INDEX index_dr_rai_action_plans_on_region_id ON public.dr_rai_action_plan
 CREATE UNIQUE INDEX index_dr_rai_data_statins_on_month_date_and_aggregate_root ON public.dr_rai_data_statins USING btree (month_date, aggregate_root);
 
 
+--
+-- Name: index_dr_rai_data_titrations_on_month_date_and_facility_name; Type: INDEX; Schema: public; Owner: -
+--
+
+CREATE UNIQUE INDEX index_dr_rai_data_titrations_on_month_date_and_facility_name ON public.dr_rai_data_titrations USING btree (month_date, facility_name);
+
+
 --
 -- Name: index_dr_rai_targets_on_dr_rai_indicators_id; Type: INDEX; Schema: public; Owner: -
 --
@@ -8778,6 +8785,7 @@ INSERT INTO "schema_migrations" (version) VALUES
 ('20250813064810'),
 ('20250814092225'),
 ('20250827134615'),
-('20250828111954');
+('20250828111954'),
+('20250923223358');