The first character that the tester should use to attempt breaking a valid SQL request is: Single quote.
SQL which full meaning is Structured Query Language is used to manage data in a computer database.
Making use of single quote character makes it possible for user to easily know whether the site is susceptible to an SQL injection.
Based on this it is important to note single quote which is also know as apostrophe is the first character that you should use in breaking a valid SQL request.
Inconclusion the first character that the tester should use to attempt breaking a valid SQL request is: Single quote.
Learn more about single quote here:https://brainly.com/question/10217528