MS Access query on linked tables with multiple joins is very slow

问题

I've a MySQL database and a MS Access front end. MySQL database tables are linked via ODBC connection to MS Access.

ANY query with multiple joined tables will run extremely slow in case of having anything in "WHERE" (or "HAVING") clause.

For example:

SELECT tblGuests.GuestName, Sum(tblPayments.Payment) AS SumOfPayment, tblRooms.RoomName
FROM (tblGuests LEFT JOIN tblPayments ON tblGuests.GuestID = tblPayments.GuestNo) LEFT JOIN tblRooms ON tblGuests.RoomNo = tblRooms.RoomID
WHERE tblGuests.NoShow=False
GROUP BY tblGuests.GuestName, tblRooms.RoomName;

will take for ages (approx. 3 minutes for 20K records.) Exactly the same script takes for 1-1.5 seconds in case of Pass Through Query, so the problem shouldn't be related to indexes or settings on server side. (By the way, indexes are set up on the necessary columns and relations are set up, too.)

The problem happens ONLY if there are more than 2 tables involved in the query AND there is something in the "WHERE" clause or in "HAVING".

For example if you modify the code above like

SELECT tblGuests.GuestName, Sum(tblPayments.Payment) AS SumOfPayment
FROM tblGuests LEFT JOIN tblPayments ON tblGuests.GuestID = tblPayments.GuestNo
WHERE tblGuests.NoShow=False
GROUP BY tblGuests.GuestName;

then it will be very quick again. (Only 2 tables are involved to the query.) Also

SELECT tblGuests.GuestName, Sum(tblPayments.HUFpayment) AS SumOfPayment, tblGuests.NoShow, tblRooms.RoomName
FROM (tblGuests LEFT JOIN tblPayments ON tblGuests.GuestID = tblPayments.GuestNo) LEFT JOIN tblRooms ON tblGuests.RoomNo = tblRooms.RoomID
GROUP BY tblGuests.GuestName, tblGuests.NoShow, tblRooms.RoomName;

will have no problem at all because there is no "WHERE" clause. However the very similar code I mentioned in the beginning of the post will be very slow, unless I run it directly on the server (or via Pass Through Query).

Do you have any idea what can cause this problem and how to avoid it (except to run Pass Through Queries all the time)?

来源：https://stackoverflow.com/questions/45666642/ms-access-query-on-linked-tables-with-multiple-joins-is-very-slow