We're trying to integrate Moodle into our organisations IT systems – which means using MS-SQL.
I'm using the new SQL Server driver for PHP version 2.

We use student id numbers as usernames. They are of the form YYnumber
Currently, unless a student id begins with 0, there is an error as follows (developer level error reporting):

Debug info: SQLState: 22018<br>
Error Code: 245<br>
Message: [Microsoft][SQL Server Native Client 10.0][SQL Server]Conversion failed when converting the nvarchar value 'guest' to data type int.<br>

SELECT * FROM bhi_user WHERE username = 9841370 AND deleted <> 1 AND mnethostid = 1
[array (
0 => '9841370',
1 => '1',
)]
Stack trace:
line 380 of \lib\dml\moodle_database.php: dml_read_exception thrown
line 261 of \lib\dml\sqlsrv_native_moodle_database.php: call to moodle_database->query_end()
line 371 of \lib\dml\sqlsrv_native_moodle_database.php: call to sqlsrv_native_moodle_database->query_end()
line 786 of \lib\dml\sqlsrv_native_moodle_database.php: call to sqlsrv_native_moodle_database->do_query()
line 864 of \lib\dml\sqlsrv_native_moodle_database.php: call to sqlsrv_native_moodle_database->get_recordset_sql()
line 1218 of \lib\dml\moodle_database.php: call to sqlsrv_native_moodle_database->get_records_sql()
line 1190 of \lib\dml\moodle_database.php: call to moodle_database->get_record_sql()
line 3812 of \lib\moodlelib.php: call to moodle_database->get_record_select()
line 3549 of \lib\moodlelib.php: call to get_complete_user_data()
line 122 of \login\index.php: call to authenticate_user_login()

I've spent some time looking into this. Originally I was confused, because the parameter array holds username as a string value.

It turns out that in lib/dlm/sqlsrv_native_moodle_database there's a call in
do_query to emulate_bound_params (line 362)
The function (line 695) seems to insert the parameters into the sql, using php type-testing functions to determine the syntax as follows
....
if ($this->is_number($param)) { // we can not use is_numeric() because it eats leading zeros from strings like 0045646
$return .= $param;
} else if (is_float($param)) {
$return .= $param;
} else {
$param = str_replace("'", "''", $param);
$return .= "N'$param'";

So if a parameter can be cast to a number it will be.
There is a note above do_query

/***

• Bound variables are supported. Until I can get it to work, emulate the bindings
• The challenge/problem/bug is that although they work, doing a SELECT SCOPE_IDENTITY()
• doesn't return a value (no result set)
  */

but I don't really know what it means

I did try changing the driver to free_tds, but couldn't get free_tds to work. Is that the direction I should be moving?