Whenever you’re adding a new field to a table, there are three important things that you’ll need to think about: data types, character limits, and validation rules. The data type determines whether the field will contain text, numbers, currency, dates, or a checkbox for simple yes or no answers. A character limit is the maximum number of characters that can be typed in a field. A validation rule allows you to limit the types of data with even more specificity. Generally, you will make these decisions when you first create a field, although it is possible to change them even if the field already contains data.
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