One of the most popular (frequently occurring rather than best liked) problems we get is with SQL strings being manipulated in VBA code.
The reason this is so difficult is that all the work is being done at a level of redirection. What I mean by this is that the coder is never working directly with the SQL itself, but rather with code which in turn, is relied on to produce the SQL that they are envisaging is required. It's rather similar to the problems coders have historically had dealing with pointers.
Anyway, a technique I often suggest to coders struggling with this (at any level. This happens to experienced coders too.) is to use either the
MsgBox() function, or
Debug.Print into the Immediate Pane of the debugger window, to display the value of the SQL in the string before using it (That's assuming you're not good with debugging generally. Personally I would trace to the line, then display the value prior to allowing execution of the string - See
Debugging in VBA). It's really much easier to appreciate what a SQL string is meant to do, and where there may be problems, when you can see it in its entirety, and in its true form, rather than as the code is about to create it.