I could have been noted before in this thread but I couldnt find it on my first search.
This function (odbc_num_rows) returns -1 when ODBCing to MS SQL and making it hard to get the number of rows in the returned recordset.
Two workarounds:
1. When you just need to verify that any rows returned from your query you can use select count(*) as cnt from table and then just get $row['cnt']
2. When you need to actually loop through the records this function returns number of rows in the recordset if and only if you include ORDER BY clause in your query statement.
That sounds a bit annoying but thats the work around when dealing with MS SQL odbc driver I guess.
It would be beneficial if someone explained how the Order By clause makes the difference.