Default value for text field from SQL Query

I have 6 fields, 5 fields from user input and 1 field default value from SQL query and want to insert to table when user click SAVE. Suppose the default value should be hidden text box, but don't know how to do it with phprunner.

using lookup wizard I can get default value for checkbox/radio button but user have to click it, so no auto default value. I also tried Javascript on load -> $("input[data-field='sem']").click(); but the checkbox did not auto tick.

so how to apply this concept to text field?

I read the manual but I can't figure out how to insert value from SQL query for the default text field.

So I try different approach using the BeforeAdd event,
This is roughly from what i have been trying to do. AND i don't know where to place this code.

~Testing no.1~
$rs = DB::Query("SELECT sem as c FROM semester WHERE CURTIME() BETWEEN mula AND akhir AND student_id= " . $_SESSION["UserID"]);
$data = $rs.fetchAssoc();
$count = $data["c"];

$data = array();
$data["sem"] = $count;
DB::Insert("laporan", $data );

~Testing no.2~
$zip = DB::DBLookup("SELECT sem FROM semester WHERE CURTIME() BETWEEN mula AND akhir AND student_id= " . $_SESSION["UserID"]);

$data = array();
$data["sem"] = $zip;
DB::Insert("laporan", $data );

this SQL query will get value for what semester the student are in for this particular month/year

If some one could guide me to a documentation on step by step to do this would be really appreciated. Thank you.