Database Reference
In-Depth Information
ically set the Length element for any data type, you should be aware that some RDBMS
programs do not allow you to specify a length for a numeric field. Instead, the RDBMS
programsetsthelengthofanumericfieldbasedonthe
type
ofnumberthefieldstores,such
as an integer, a long integer, or a real number.
Decimal Places
This denotes the number of digits to the
right
of the decimal point in a real number. The
numberofdigitsdeterminestherealnumber'sprecision.Forexample,manybusinessesre-
quire that all currency values have four digits of precision to the right of the decimal point.
Character Support
This element indicates the type of characters that a user can enter into a given field value.
Setting and enforcing this element helps you ensure that the user cannot introduce mean-
ingless data into the field, thus enhancing
field-level integrity.
Let's say you're working with a C
UST
S
TATE
field and its data type is alphanumeric. This
datatypeisappropriateforthefieldbecauseitallowsausertoincorporatelettersaspartof
a given field value. But it also allows him to use numbers, keyboard characters, and exten-
dedcharacters, whichmeansthathecanenterameaningless valueintothefield—thereare
no state names or state abbreviations that contain characters other than letters. You solve
this problem by using the Character Support element to define the characters that the user
can incorporate within a field value. (Iaddress the issue ofa
valid
combination ofletters in
the “
Logical Elements
”
section.)
You can choose to include or exclude any of the following types of characters.
•
Letters:
All letters of the alphabet
including
foreign language letters such as é and
ñ.
•
Numbers:
0 through 9.
•
Keyboard characters:
Any standard character other than letters and numbers, such
as asterisk, ampersand, bracket, caret, comma, equals sign, exclamation point, par-
enthesis, percent sign, period, pound sign, question mark, quote, semicolon, slash,
or vertical bar. Note that the Field Specifications sheet includes examples of the
characters that belong to this category.
•
Special characters:
Any character that you can produce only through specific com-
binations of standard keys and the CTRL, ALT, and/or SHIFT keys, or with the aid
of a special software program. Characters in this category include complex math-
ematical symbols, the copyright symbol, fractions, the symbol for pi, and the trade-
mark symbol. The Field Specifications sheet includes examples of these characters
as well.
