fix: speed up the listPastEvents query ⚡️

packages/core/src/modules/events/events.ts

@@ -199,25 +199,55 @@ type ListPastEventsInput = {
 export async function listPastEvents({ timezone }: ListPastEventsInput) {
   const records = await db
     .selectFrom('events')
-    .leftJoin('eventAttendees', 'eventAttendees.eventId', 'events.id')
-    .leftJoin('students', 'students.id', 'eventAttendees.studentId')
+    .leftJoin(
+      (eb) => {
+        return eb
+          .selectFrom('eventAttendees')
+          .select(['eventId', ({ fn }) => fn.count('email').as('attendees')])
+          .groupBy('eventId')
+          .as('attendees');
+      },
+      (join) => {
+        return join.onRef('attendees.eventId', '=', 'events.id');
+      }
+    )
+    .leftJoin(
+      (eb) => {
+        return eb
+          .selectFrom('eventAttendees')
+          .leftJoin('students', 'students.id', 'eventAttendees.studentId')
+          .select([
+            'eventId',
+            'profilePicture',
+            ({ ref }) => {
+              const field = sql<number>`row_number() over (partition by ${ref('eventId')} order by ${ref('eventAttendees.createdAt')} asc)`;
+
+              return field.as('rank');
+            },
+          ])
+          .where('students.profilePicture', 'is not', null)
+          .as('pictures');
+      },
+      (join) => {
+        return join
+          .onRef('pictures.eventId', '=', 'events.id')
+          .on('pictures.rank', '<=', 3);
+      }
+    )
     .select([
       'events.endTime',
       'events.id',
       'events.name',
       'events.recordingLink',
       'events.startTime',
+      ({ fn }) => {
+        return fn.max('attendees.attendees').as('attendeesCount');
+      },
       ({ ref }) => {
-        const field = sql<string>`string_agg(${ref('students.profilePicture')}, ',' order by ${ref('eventAttendees.createdAt')} asc)`;
+        const field = sql<string>`string_agg(${ref('profilePicture')}, ',')`;
 
         return field.as('profilePictures');
       },
-      ({ fn }) => {
-        return fn
-          .count<string>('eventAttendees.email')
-          .distinct()
-          .as('attendeesCount');
-      },
     ])
     .where('events.endTime', '<=', new Date())
     .where('events.hidden', '=', false)
@@ -240,8 +270,7 @@ export async function listPastEvents({ timezone }: ListPastEventsInput) {
 
       const profilePictures = (_profilePictures || '')
         .split(',')
-        .filter(Boolean)
-        .slice(0, 3);
+        .filter(Boolean);
 
       return {
         ...record,