Test if returns values before return

In a stored procedure called by a VB.NET program, I build an SQL statement then use EXEC sp_executesql @SQL to run it.  I am selecting from one column based on certain criteria, but if this would return no values, I want to build the select statement from a second column and then return those values instead.  How can I test how many records an @SQL statement will return before returning it? 

A simplified version of my code is below.  If this returns records, I want to return these.  If If this returns no records, I want to replace ' WHERE V1 IN (SELECT MAX(V1)..." with 'WHERE V2 IN (SELECT MAX(V2)..."  and then return those results.  Any suggestions on how to best accomplish this?

SET @SQL = 'SELECT * FROM ' + @MyTable + ' WHERE V1 IN (SELECT MAX(V1) FROM ' + @MyTable + ' WHERE T1 = @T1 AND C1 = @C1)'

EXEC sp_execute @SQL

" N'@T1 nvarchar(255), @C1 nvarchar(255)',
  @T1, @C1"
RETURN

Gina