I don't think I explained myself very well anyway.

There are OLE connection strings that can be used to access an Excel spreadsheet
as though it is a database. See, for instance,
http://www.connectionstrings.com/, and scroll down to the Excel ones.

You can access ODBC connections from Excel using connection strings.

So I'd expect that one Excel workbook  could cheerfully access another Excel
workbook using an ODBC connection and SQL statements.

But ... I doubt that a workbook could access ITSELF using SQL statements. It
might possibly be able to access the disk copy of itself, although I suspect
that even this would give file access contention for SQL statements that update
the file.

I've never tried to link Excel to Excel in this way, nor do I anticipate wanting
to do so. In the past, I've certainly linked to Excel from Access (although I
simply mapped the spreadsheet as a table, rather than using an ODBC connection
string and VBA code).

I am currently updating a system that accesses Sybase databases from Excel using
appropriate connection strings. For testing at home, I swap the connection
string to an Access one, and thus have Excel using SQL to manipulate an Access
database.