SQL injection attacks are when an attacker uses a web form field or URL parameter to gain access to or manipulate your database. When you use standard Transact SQL it is easy to unknowingly insert rogue code into your query that could be used to change tables, get information and delete data. You can easily prevent this by always using parameterised queries, most web languages have this feature and it is easy to implement.
Consider this query:
"SELECT * FROM table WHERE column = '" + parameter + "';"
If an attacker changed the URL parameter to pass in ' or '1'='1 this will cause the query to look like this:
"SELECT * FROM table WHERE column = '' OR '1'='1';"
Since '1' is equal to '1' this will allow the attacker to add an additional query to the end of the SQL statement which will also be executed.
You could fix this query by explicitly parameterising it. For example, if you're using MySQLi in PHP this should become:
$stmt = $pdo->prepare('SELECT * FROM table WHERE column = :value');
$stmt->execute(array('value' => $parameter));
Get from: https://www.creativebloq.com/web-design/website-security-tips-protect-your-site-7122853