WHERE-clause for last non-null value - mysql

Question

I'm making a community database for a school project and have ran into an issue. I am attempting to integrate a log system but retrieve the latest non-null value from column in a table called logs and present that information on a different page. My current code (without any attempt at filtering by their rank) looks as follows:
SELECT m.MemberID, m.MemberName, o.OfficeID, o.OfficeDesignation, p.PositionAbbreviation, l.LogRank
FROM logs l
INNER JOIN (SELECT l.LogMember, MAX(l.LogDate) AS maxLogDate FROM logs l GROUP BY l.LogMember) l2
ON (l.LogMember = l2.LogMember AND l.LogDate = l2.maxLogDate)
INNER JOIN members m
ON (l.LogMember = m.MemberID)
INNER JOIN offices o
ON (l.LogOffice = o.OfficeID)
INNER JOIN positions p
ON (l.LogPosition = p.PositionID)
GROUP BY m.MemberID;
The above query returns the latest entry for each member in the logs table, but I can't figure out how to, when l.LogRank returns NULL, take the latest non-null value only for that column.
I have struggled with a variety of approaches to this problem over the past week to no avail. Any help/pointers would be appreciated.
EDIT: Sample data seen below:
+-------+-----------+---------+-----------+-------------+-----------+
| LogID | LogMember | LogRank | LogOffice | LogPosition | LogDate |
+-------+-----------+---------+-----------+-------------+-----------+
| 1 | 1 | 1 | 7 | 5 | TIMESTAMP |
+-------+-----------+---------+-----------+-------------+-----------+
| 2 | 1 | 1 | | 1 | TIMESTAMP |
+-------+-----------+---------+-----------+-------------+-----------+
| 3 | 1 | | 1 | | TIMESTAMP |
+-------+-----------+---------+-----------+-------------+-----------+
The various INT values reference IDs in the relevant other tables.
Desired Output:
+-------+-----------+---------+-------------------+-----------------+-----------+
| LogID | LogMember | LogRank | OfficeDesignation | PositionAbbrev. | LogDate |
+-------+-----------+---------+-------------------+-----------------+-----------+
| 1 | 1 | 1 | C-6 | CO | TIMESTAMP |
+-------+-----------+---------+-------------------+-----------------+-----------+
So basically I want to retrieve the MemberID, MemberName, OfficeID, OfficeDesignation, PositionAbbreviation, and LogRank from a variety of tables and get the latest non-null record for each column.

Answer 1

INNER JOIN (
SELECT l.LogMember, l.LogRank FROM logs l
WHERE l.LogDate=(
SELECT LogDate FROM logs
WHERE LogMember=l.LogMember
AND LogRank IS NOT NULL
ORDER BY LogDate DESC
LIMIT 1
)
) l3
ON (l.LogMember = l3.LogMember)