DROP indexes before recreating them

synapse/storage/schema/delta/16/unique_constraints.sql

@@ -6,6 +6,7 @@ DELETE FROM current_state_events WHERE rowid not in (
     SELECT MIN(rowid) FROM current_state_events GROUP BY event_id
 );
 
+DROP INDEX IF EXISTS current_state_events_event_id;
 CREATE UNIQUE INDEX current_state_events_event_id ON current_state_events(event_id);
 
 --
@@ -13,6 +14,7 @@ DELETE FROM room_memberships WHERE rowid not in (
     SELECT MIN(rowid) FROM room_memberships GROUP BY event_id
 );
 
+DROP INDEX IF EXISTS room_memberships_event_id;
 CREATE UNIQUE INDEX room_memberships_event_id ON room_memberships(event_id);
 
 --
@@ -20,6 +22,7 @@ DELETE FROM feedback WHERE rowid not in (
     SELECT MIN(rowid) FROM feedback GROUP BY event_id
 );
 
+DROP INDEX IF EXISTS feedback_event_id;
 CREATE UNIQUE INDEX feedback_event_id ON feedback(event_id);
 
 --
@@ -27,6 +30,7 @@ DELETE FROM topics WHERE rowid not in (
     SELECT MIN(rowid) FROM topics GROUP BY event_id
 );
 
+DROP INDEX IF EXISTS topics_event_id;
 CREATE UNIQUE INDEX topics_event_id ON topics(event_id);
 
 --
@@ -34,6 +38,7 @@ DELETE FROM room_names WHERE rowid not in (
     SELECT MIN(rowid) FROM room_names GROUP BY event_id
 );
 
+DROP INDEX IF EXISTS room_names_id;
 CREATE UNIQUE INDEX room_names_id ON room_names(event_id);
 
 --
@@ -41,6 +46,7 @@ DELETE FROM presence WHERE rowid not in (
     SELECT MIN(rowid) FROM presence GROUP BY user_id
 );
 
+DROP INDEX IF EXISTS presence_id;
 CREATE UNIQUE INDEX presence_id ON presence(user_id);
 
 --
@@ -49,6 +55,7 @@ DELETE FROM presence_allow_inbound WHERE rowid not in (
     GROUP BY observed_user_id, observer_user_id
 );
 
+DROP INDEX IF EXISTS presence_allow_inbound_observers;
 CREATE UNIQUE INDEX presence_allow_inbound_observers ON presence_allow_inbound(
     observed_user_id, observer_user_id
 );
@@ -59,6 +66,7 @@ DELETE FROM presence_list WHERE rowid not in (
     GROUP BY user_id, observed_user_id
 );
 
+DROP INDEX IF EXISTS presence_list_observers;
 CREATE UNIQUE INDEX presence_list_observers ON presence_list(
     user_id, observed_user_id
 );