add daydiff function query

lib/prisma.ts

@@ -34,6 +34,18 @@ function getAddMinutesQuery(field: string, minutes: number): string {
   }
 }
 
+function getDayDiffQuery(field1: string, field2: string): string {
+  const db = getDatabaseType(process.env.DATABASE_URL);
+
+  if (db === POSTGRESQL) {
+    return `${field1}::date - ${field2}::date`;
+  }
+
+  if (db === MYSQL) {
+    return `DATEDIFF(${field1}, ${field2});`;
+  }
+}
+
 function getDateQuery(field: string, unit: string, timezone?: string): string {
   const db = getDatabaseType();
 
@@ -180,6 +192,7 @@ function getPageFilters(filters: SearchFilter<any>): [
 export default {
   ...prisma,
   getAddMinutesQuery,
+  getDayDiffQuery,
   getDateQuery,
   getTimestampIntervalQuery,
   getFilterQuery,

queries/analytics/reports/getRetention.ts

@@ -33,7 +33,7 @@ async function relationalQuery(
   }[]
 > {
   const { startDate, endDate } = dateRange;
-  const { getDateQuery, rawQuery } = prisma;
+  const { getDateQuery, getDayDiffQuery, rawQuery } = prisma;
   const timezone = 'utc';
   const unit = 'day';
 
@@ -49,7 +49,10 @@ async function relationalQuery(
     user_activities AS (
       select distinct
         w.session_id,
-        (${getDateQuery('created_at', unit, timezone)}::date - c.cohort_date::date) as day_number
+        (${getDayDiffQuery(
+          getDateQuery('created_at', unit, timezone),
+          'c.cohort_date',
+        )}) as day_number
       from website_event w
       join cohort_items c
       on w.session_id = c.session_id