student_id	fname	lname	day_enrolled	age	username
1	Sky	Towner	2015-12-03	17	stowner1
2	Ben	Davis	2016-04-20	19	bdavis2
3	Travis	Apple	2018-08-14	18	tapple3
4	Arthur	David	2016-04-01	16	adavid4
5	Benjamin	Town	2014-01-01	17	btown5

The above sample table can be created using the code here.

To update records in this table that contain the string 'dav' in their username and replace it with 'DAV':


        
        
            
                
                
                    UPDATE students
SET username = REPLACE(username, 'dav', 'DAV');

SELECT * FROM students;
                
            
            +------------+----------+--------+--------------+------+----------+
| student_id | fname    | lname  | day_enrolled | age  | username |
+------------+----------+--------+--------------+------+----------+
|          1 | Sky      | Towner | 2015-12-03   |   17 | stowner1 |
|          2 | Ben      | Davis  | 2016-04-20   |   19 | bDAVis2  |
|          3 | Travis   | Apple  | 2018-08-14   |   18 | tapple3  |
|          4 | Arthur   | David  | 2016-04-01   |   16 | aDAVid4  |
|          5 | Benjamin | Town   | 2014-01-01   |   17 | btown5   |
+------------+----------+--------+--------------+------+----------+