In-Band SQL Injection
In-Band SQL Injection is the easiest type to detect and exploit; In-Band just refers to the same method of communication being used to exploit the vulnerability and also receive the results, for example, discovering an SQL Injection vulnerability on a website page and then being able to extract data from the database to the same page.
Error-Based SQL Injection
This type of SQL Injection is the most useful for easily obtaining information about the database structure as error messages from the database are printed directly to the browser screen. This can often be used to enumerate a whole database.
Union-Based SQL Injection
This type of Injection utilises the SQL UNION operator alongside a SELECT statement to return additional results to the page. This method is the most common way of extracting large amounts of data via an SQL Injection vulnerability.
Out-of-Band SQL Injection
Out-of-Band SQL Injection isn't as common as it either depends on specific features being enabled on the database server or the web application's business logic, which makes some kind of external network call based on the results from an SQL query.