Which input validation method ensures that data has been entered?

The presence check is an input validation method specifically designed to verify that data has been entered into a field. When this check is applied, it ensures that the user cannot submit a form or complete a function unless they have provided a response for a particular input. This is particularly important in scenarios where certain information is mandatory for the system to function correctly, like a user registration form requiring an email address.

In contrast, other validation methods serve different purposes. A look-up table checks whether entered data matches a predefined set of values, which may not necessarily confirm that information is present; it only verifies the correctness of the value if one has been input. Length checks focus on ensuring that the data entered conforms to a specified number of characters, which again does not guarantee that any data has been entered. Syntax checks, on the other hand, validate the format of the data entered, checking for adherence to a set pattern (like email format) but do not ensure that the field is filled out.

Therefore, the presence check is the most suitable method for verifying that data has indeed been provided.