To improve efficiency of my main form across a network I have set its 
Recordsource to

SELECT * FROM MyTable WHERE RecID = " & tmpID

TmpID is initially set to zero so the form opens with no data. After that 
it is set using a lookup of recent RecIDs

The main form has a Sub Form showing records from another table 
(MySubTable) linked in a one to many relationship to MyTable. At the moment 
this Sub Form's recordsource is set to the table name (MySubTable) and is 
linked to the main table via the Master Child properties on RecID

What is Access doing with the Sub Form's recordsource when RecID changes in 
the main table?

1. Does it pull the entire table across the network and then filter it 
according to RecID
2. Does it construct its own SQL statement to just pull across the SubTable 
records that have the correct RecID.

If 1 then maybe I should use an SQL statement to get the sub table data as 
well.
If 2 then I won't get any performance improvement from this.

Any ideas?
Thanks
Mike