Discard last 3 characters of a field in MySQL

Let us first create a table −

mysql> create table DemoTable
   -> (
   -> StudentId varchar(100)
   -> );
Query OK, 0 rows affected (0.58 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable values('STU-090');
Query OK, 1 row affected (0.16 sec)

mysql> insert into DemoTable values('STU-123');
Query OK, 1 row affected (0.15 sec)

mysql> insert into DemoTable values('STU-678');
Query OK, 1 row affected (0.29 sec)

Display all records from the table using select statement −

mysql> select *from DemoTable;

Output

This will produce the following output −

+-----------+
| StudentId |
+-----------+
| STU-090   |
| STU-123   |
| STU-678   |
+-----------+
3 rows in set (0.00 sec)

Following is the query to discard last 3 characters of a field −

mysql> SELECT REVERSE(SUBSTR(REVERSE(StudentId), 4)) from DemoTable

Output

This will produce the following output −

+----------------------------------------+
| REVERSE(SUBSTR(REVERSE(StudentId), 4)) |
+----------------------------------------+
| STU-                                   |
| STU-                                   |
| STU-                                   |
+----------------------------------------+
3 rows in set (0.00 sec)