Purpose

If you are an administrator of Confluence and you'd like to list all of the Calendars your Confluence users had subscribed to in your Confluence instance, you may then use the following query. 

Solution

To list all of the Calendars your users had subscribed to in your Confluence instance, together with the subscription date:

The following query was tested on PostgreSQL.

SELECT um."username" AS "Username", tc."NAME" AS "Calendar Name", to_timestamp(CAST(tc."CREATED" AS bigint)/1000) AS "Subscription Date" FROM "AO_950DC3_TC_SUBCALS" tc
LEFT JOIN "user_mapping" um ON um."user_key" = tc."CREATOR"
WHERE tc."CREATOR" = um."user_key"
AND "PARENT_ID" IS NULL
AND "SUBSCRIPTION_ID" IS NOT NULL;

 The "SUBSCRIPTION_ID" IS NOT NULL will filter out the Creator of the calendar. If you wish to get the result together with the Creator of the calendar, you can remove the line.