There are different methods and techniques that hackers would use to attack a database. One of the common security attacks is through SQL injection. This method is often used on websites by inserting SQL statements on one of the input boxes of a web form 
that would perform certain commands on the backend. If a website is badly designed where such attacks are not considered during design, then there is a high risk of getting data in wrong hands.
What is SQL injection testing?
SQL injection testing is a technique that is meant to check if a site’s input fields/web form has vulnerabilities that can be exploited to retrieve info/attack its database. SQL injection can be performed in several ways. A user can enter an input with an embedded SQL statement where the system will not be able to detect the string literal escape characters. Another way can be when the system is not strongly typed which would specify the different data types that can be used in a certain input. If this weakness is discovered by a malicious user, database information can then be manipulated by the attacker as (s)he sees fit.
How to prevent SQL Injection Attacks?
One of the basic ways a developer can protect his system is to always validate all user inputs. Validations of user input should include the input type, format, length and the range. The developer should be able to anticipate such attacks so as to craft their codes in such a way that would stop attacks before it can happen. That is why it is also important to do software testing before any program is implemented in public. This way, such attacks can be simulated in a controlled environment and no actual data will be harmed.
When testing websites, it is important to check the data type and the size of input. This way such features can already limit the possibility of a SQL injection through buffer overruns. Also, it is important to accept expected values such as when one is expecting an email input. When a developer is working with XML documents, it is always best to validate all data input against the specified XML schema. Also, it will be best to make use of stored procedures to validate input of users.
There are a lot of techniques that can be used by the developer and testers to ensure that their websites and web applications are safe from SQL injection. It is important to have functions and methods present that will validate user input strings on entry. Following the best practices will ensure companies from incurring grave losses resulting from SQL injection attacks. Wikipedia has a nice writeup on SQL injection.