In php, we have two option to concatenate table columns.
First Option using Query
In query, CONCAT keyword used to concatenate two columns
SELECT CONCAT(`SUBJECT`,'_', `YEAR`) AS subject_year FROM `table_name`;
Second Option using symbol ( . )
After fetch the data from database table, assign the values to variable, then using ( . ) Symbol and concatenate the values
$subject = $row['SUBJECT'];
$year = $row['YEAR'];
$subject_year = $subject . "_" . $year;
Instead of underscore( _ ) , we will use the spaces, comma, letters,numbers..etc