Access validates certain types of data automatically. Therefore, you don’t have to enter any data-validation rules for these data types when you specify table properties. The data types that Access validates automatically include

• Number/Currency
• Date/Time
• Yes/No

Access validates the data type when you move off the field. When you enter a letter into a Number or Currency field, you don’t initially see a warning not to enter these characters. However, when you tab out of or click on a different field, you get a warning like the one shown in Figure 34-25. This particular warning lets you choose to enter a new value or change the column’s data type to Text. You’ll see this message if you enter other inappropriate characters (symbols, letters, and so on), enter more than one decimal point, or enter a number too large for a certain Number data type.

FIGURE 34-25
The warning Access displays when entering data that doesn’t match the field’s data type. Access gives you a few choices to correct the problem.

Access validates Date/Time fields for valid date or time values. You’ll see a warning similar to the one, if you try to enter a date such as 14/45/05, a time such as 37:39:12, or an invalid character in a Date/Time field.

Yes/No fields require that you enter one of these defined values: Yes, True, -1, or a number other than 0 (it displays as a -1) for Yes; or No, False, Off, or 0 for No. Of course, you can define your own acceptable values in the Format property for the field, but generally these are the only acceptable values. If you enter an invalid value, the warning appears with the message to indicate an inappropriate value.

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