When a user designs a table in exTables he has the option to create validation rules which new entries to the table must fulfill. These rules can be to prevent empty columns, validate the format of the input, force user to input values under/between/over certain constants or many more specific ways to validate that the new entry fits to the table design.
Rows with validation errors are red with a error icon shown in the indicator column on the left.
How to create validation rules
Validation rules are created using SQL action which updates the system column [__ValidationError] with the appropriate error message.
Enabling Automatically run when saving data and Refresh data after execution are very handy features for validation rules as it ensures validation is always performed when user saves and that rows with validation errors are properly displayed to the user afterwards