Microsoft Access 2010 Bible

Part I: Access Building Blocks

52

Memo data type

The Memo data type holds a variable amount of data from 0 to 65,536 characters for each record.

So, if one record uses 100 characters, another requires only 10, and yet another needs 3,000, you

use only as much space as each record requires.

You don’t specify a field size for the Memo data type. Access allocates as much space as necessary

for the memo data.

Number data type

The Number data type enables you to enter numeric data — that is, numbers that will be used in

mathematical calculations or represent scalar quantities such as inventory counts. (If you have data

that will be used in monetary calculations, you should use the Currency data type, which performs

calculations without rounding errors.)

The exact type of numeric data stored in a number field is determined by the Field Size prop-

erty. Table 2.3 lists the various numeric data types, their maximum and minimum ranges, the deci-

mal points supported by each numeric data type, and the storage (bytes) required by each numeric

data type.

TABLE 2.3

Numeric Field Settings

Field Size Setting Range Decimal Places Storage Size

Byte 0 to 255 None 1 byte

Integer –32,768 to 32,767 None 2 bytes

Long Integer –2,147,483,648 to 2,147,483,647 None 4 bytes

Double –1.797 × 10308 to 1.797 × 10308 15 8 bytes

Single –3.4 × 1038 to 3.4 × 1038 7 4 bytes

Replication ID N/A N/A 16 bytes

Decimal 1–28 precision 15 8 bytes

Caution
Many errors are caused by choosing the wrong numeric type for number fields. For example, notice that the
maximum value for the Integer data type is 32,767. I once saw a database that ran perfectly for several
years and then started crashing with overflow errors. It turned out that the overflow was caused by a particular
field being set to the Integer data type, and when the company occasionally processed very large orders, the
32,767 maximum was exceeded.

Be aware that overflow may occur simply by adding two numbers together, or performing any mathematical
operation that results in a value too large to be stored in a field. Some of the most difficult bugs occur only
when circumstances (such as adding or multiplying two numbers) cause an overflow condition at runtime.