Look at the example above again. The original purpose of the code was to create an SQL statement to select a user, with a given user id.
If there is nothing to prevent a user from entering "wrong" input, the user can enter some "smart" input like this:
UserId:
Then, the SQL statement will look like this:
SELECT * FROM Users WHERE UserId = 105 OR 1=1;
The SQL above is valid and will return ALL rows from the "Users" table, since OR 1=1 is always TRUE.
Does the example above look dangerous? What if the "Users" table contains names and passwords?
The SQL statement above is much the same as this:
SELECT UserId, Name, Password FROM Users WHERE UserId = 105 or 1=1;
A hacker might get access to all the user names and passwords in a database, by simply inserting 105 OR 1=1 into the input field.
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