How can I create MySQL stored procedure with OUT parameter?

To make it understand we are using the table named ‘student_info’ which have the following values −

mysql> Select * from student_info;
+------+---------+------------+------------+
| id   | Name    | Address    | Subject    |
+------+---------+------------+------------+
| 101  | YashPal | Amritsar   | History    |
| 105  | Gaurav  | Jaipur     | Literature |
| 110  | Rahul   | Chandigarh | History    |
| 125  | Raman   | Shimla     | Computers  |
+------+---------+------------+------------+
4 rows in set (0.00 sec)

Now, with the help of the following query, we will create a stored procedure with OUT parameter which will count the total of a particular subject by providing the subject name as the parameter.

mysql> DELIMITER // ;
mysql> Create Procedure subjects (IN S_Subject VARCHAR(25), OUT total INT)
   -> BEGIN
   -> SELECT count(subject)
   -> INTO total
   -> FROM student_info
   -> WHERE subject = S_subject;
   -> END //
Query OK, 0 rows affected (0.00 sec)

mysql> DELIMITER ;

‘S-Subject’ is the IN parameter that is the number of subjects we want to count and ‘total’ is the OUT parameter that stores the number of subjects for a particular subject.

mysql> CALL subjects('Computers', @total);
Query OK, 1 row affected (0.02 sec)

mysql> Select @total;
+--------+
| @total |
+--------+
|      1 |
+--------+
1 row in set (0.01 sec)

mysql> CALL subjects('History', @total);
Query OK, 1 row affected (0.00 sec)

mysql> Select @total;
+--------+
| @total |
+--------+
|      2 |
+--------+
1 row in set (0.00 sec)