Question

I have a query that produces a result like this:

The data is sorted by date DESC, then by time DESC, but also the common ‘markers_name’ elements are chunked together. (They’re only chunked together for each date).

To do this I get the list of MAX(time) values for every combination of (markers_id, date) in conditions, then join that list to the row set I am getting from the present query, and use the MAX(time) values for sorting:

SELECT
  m.name AS markers_name,
  c.time AS conditions_time,
  c.date AS conditions_date,
  s.name AS station_name
FROM markers m
  INNER JOIN conditions c ON c.markers_id = m.id
  INNER JOIN station s    ON c.station_id = s.id
  INNER JOIN (
    SELECT
      markers_id,
      date,
      MAX(time) AS time
    FROM conditions
    GROUP BY
      markers_id,
      date
  ) mx ON c.markers_id = mx.markers_id AND c.date = mx.date
ORDER BY
  c.date DESC,
  mx.time DESC,
  m.name DESC,
  c.time DESC

Now I need to restrict user access to some of the rows.
The conditions table has a ‘private’ column. If ‘private’ is set to 1 only some people are allowed to see the query row. The people that can see it include the person that created the conditions report and that person’s contacts. The conditions table has a ‘user_id’, which contains the id of the person that created the conditions report. The contacts are obtained from a ‘contacts’ table which has two fields: ‘user_id’ and ‘friend_id’. I have the user_id of the person requesting the information.

To restate another way, I need to do something like this:

1. Do the query above, but also check to see if c.private is set to one.
2. If c.private is set to one use c.user_id to get that user’s ‘friend_id’s from the contacts table.
3. If the user_id of the person requesting the information matches c.user_id or any of c.user_id’s friends return the query row. If not, don’t return that row or return something that indicates that the row is private (I could have a markers_name with the name “Private” in the database, for example.

If anyone has any ideas I would love to hear them. I struggled with this all day yesterday. Thank you.

Answer 1

Possibly just adding a filter like this would be enough:

…
WHERE c.Private <> 1
   OR c.user_id = @user_id
   OR c.user_id IN (
     SELECT friend_id
     FROM contacts WHERE user_id = @user_id
   )

where @user_id is the ID of the person requesting the info.

This would prohibit the private rows from appearing in the output where inappropriate.

If, however, you’d rather like them to be there but be marked as Private (for being dealt with later in the client or something like that), you could use that filter as a column in your SELECT clause:

SELECT
  NOT (
    c.Private <> 1
    OR c.user_id = @user_id
    OR c.user_id IN (
      SELECT friend_id
      FROM contacts WHERE user_id = @user_id
    )
  ) AS IsPrivate,
  …
FROM …