This might be what you are looking for. Use three queries and then a union
query.
PatChavie_BkKeeperClient --
SELECT [Pat Chavie].BookKeeper, [Pat Chavie].Client, Avg([Pat Chavie].Entry)
AS AvgOfEntry
FROM [Pat Chavie]
GROUP BY [Pat Chavie].BookKeeper, [Pat Chavie].Client;
PatChavie_Client --
SELECT [Pat Chavie].Client, Avg([Pat Chavie].Entry) AS AvgOfEntry
FROM [Pat Chavie]
GROUP BY [Pat Chavie].Client;
PatChavie_BkKeeper --
SELECT [Pat Chavie].BookKeeper, Avg([Pat Chavie].Entry) AS AvgOfEntry
FROM [Pat Chavie]
GROUP BY [Pat Chavie].BookKeeper;
UNION QUERY --
SELECT PatChavie_BkKeeperClient.BookKeeper, PatChavie_BkKeeperClient.Client,
PatChavie_BkKeeperClient.AvgOfEntry
FROM PatChavie_BkKeeperClient
UNION ALL SELECT PatChavie_BkKeeper.BookKeeper,NULL ,
PatChavie_BkKeeper.AvgOfEntry
FROM PatChavie_BkKeeper
UNION ALL SELECT NULL, PatChavie_Client.Client, PatChavie_Client.AvgOfEntry
FROM PatChavie_Client;