docs: Document beforeafter SQL function (#2364)

MAP-1676

helm_deploy/REPORTS.md

@@ -4,6 +4,7 @@ With the exception of the Monthly Incomplete PER Report (see below) new jobs can
 
 ***Note: Where possible, use the read-replica database.*** The SQL in the configuration is executed directly against the database.
 
+
 # CronJob File
 Most of the cronjob can be copied wholesale when adding new reports, replacing the following as required:
 
@@ -13,6 +14,7 @@ The name of the configmap should match that of the `metadata.name` in the respec
 
 `spec.schedule` should be changed as needed. This is in UTC and as such will run at eg 8.30 AM in Summer when defined as `30 7 * * *` 
 
+
 # Config file:
 
 Fields in the config file define the report and the content of the email.
@@ -28,7 +30,6 @@ Fields in the config file define the report and the content of the email.
 - report_sql: The SQL to run against the database. Use the placeholders `[FROM]` and `[TO]` to have the dates defined in the `from-date` and `to-date` keys subsituted in in the format `'YYY-MM-DD'`
 
 
-
 # Placeholders
 
 As described above, the SQL script will have any `[FROM]` or `[TO]` placeholders replaced by the date interpeted from the `from-date` and `to-date` keys in the config.
@@ -43,8 +44,34 @@ These dates and the current day's date are also available to be used in the emai
 - `[LAST_MONTH]`  Last month's name and year eg `April 2023`
 
 
-
 # Monthly Incomplete PER report
 
 This report shouldn't be used as a template for creating any one-file reports as it is scripted differently to allow for multiple queries to be run before being combined as sheets in an xlsx.
-It still uses parts of the scripts in `00-reporting-scripts` so changes to those will affect all reports.
+It still uses parts of the scripts in `00-reporting-scripts` so changes to those will affect all reports.
+
+
+# Required function
+
+For the weekly cancelled move reports to work, this function must exist in the database:
+
+```
+CREATE OR REPLACE FUNCTION public.beforeafter(
+	interval)
+    RETURNS character varying
+    LANGUAGE 'plpgsql'
+    COST 100
+    VOLATILE PARALLEL UNSAFE
+AS $BODY$
+BEGIN
+	if $1 > interval '0 seconds' then
+	   return 'Before cutoff ('|| $1 || ')';
+	else
+	   return 'After cutoff (' || ($1 * -1)  || ')';
+	   end if;
+
+END;
+$BODY$;
+
+ALTER FUNCTION public.beforeafter(interval)
+    OWNER TO "cpLOUozNLn";
+```