1. Attributes and Domains
Attribute Data Types
Numeric Data Types
Text Data Types
Date Data Types
Other Data Types
Domain Constraints

2. Non-key Attributes
Previous discussion has focused on different kinds of attributes
Primary keys
Foreign keys
Alternate keys (candidate keys)
We have implied and sometimes illustrated other attributes
Attributes that just contain information we want to record about an entity
Do not serve as any sort of key

3. Non-key Attributes (cont.)
Four major issues with non-key attributes
Identifying descriptive attributes
Placing attributes in the correct entity
Rules of normalization
Appropriate functional dependency
Identifying the appropriate data type for the attribute (field)
Specifying appropriate domain business rules for the attribute (field)

4. Attribute Data Types
When attributes are instantiated in a database they become fields
Fields must have a data type
Similar to variable type in programming
(Variants are not allowed)
Data type specifies:
Class of data (numeric, text, date, binary, other)
Size of data within the class

5. Attribute Data Types (cont.)
A field’s type supports processing and storage efficiency
Storage
The number 123 can be represented with one byte
The text “123” requires three bytes
Processing
“123” must be converted to a number before it can be used in an arithmetic calculation
The number 123 can be used directly in an arithmetic calculation

6. Attribute Data Types (cont.)
Many DB operations require comparisons of values
Computers perform numeric operations (comparisons and arithmetic) much more efficiently than textual comparisons or text operations
But a tremendous amount of useful business data is textual
Date values are stored and compared as numbers but displayed as conventional dates
Choose the appropriate data type for your attribute

7. Attribute Data Types (cont.)
Some special cases
Leading zeros in numbers
‘Numeric’ fields such as zip codes and social security numbers can start with zeros
Storing them as numbers will strip off the leading zeros
Store as text to retain leading zeros
(And you will rarely perform arithmetic on them)
International implications
Many countries use letters in their postal (zip) codes

8. Numeric Data Types in SQL Server 2000
Integers
bigint Integers from -2^63 to 2^63 – 1 (8 bytes)
int Integers from -2^31 to 2^31 – 1 (4 bytes)
smallint Integers from -2^15 to 2^15 – 1 (2 bytes)
tinyint Integers from 0 to (1 byte)
Note: only positive for tinyint
bit 0 or 1 only
Used for boolean values
No True/False data type in SQL Server

9. Numeric Data Types in SQL Server 2000 (cont.)
Decimal numeric values
Money and SmallMoney are the workhorses of business programming
money
± 2^63 (~ ± 922 trillion)
decimal point fixed to four digits (1/10,000)
no monetary formatting ($ or commas)
smallmoney +/- 214, fixed to four places

10. Numeric Data Types in SQL Server 2000 (cont.)
Decimal numeric values
Decimal or Numeric types are equivalent
Allow specifying large values of decimal precision
approximate range +/- 10^38
decimal point can be anywhere in the value
Decimal(p, s)
p=1-38: Number of digits represented
s<p: Digits right of decimal place
p affects storage size
P<=9 −5 Bytes; 29 <= p <=38−17 Bytes

11. Numeric Data Types in SQL Server 2000 (cont.)
Decimal numeric values (cont.)
Float and Real
Values stored in scientific notation
Float(n) where n=number of digits in coefficient
These are very imprecise
Not commonly used in business

12. Numeric Precision
The type of numeric field also limits the size of calculated results on that field
You might choose tinyint for a quantity field in a retail application
If all quantities are summed and the result exceeds 255 the result will be limited to 255
There is a hierarchy of precedence for data type conversions
E.g., Money_value * SmallMoney_value gives a Money_value
TinyInt + SmallInt gives a SmallInt

13. Numeric Precision (cont.)
Date Precedence
DateTime
SmallDateTime
Character Precedence
nText
Text
nVarChar
VarChar
Char
Numeric Precedence
Float
Real
Decimal
Money
SmallMoney
BigInt
Int
SmallInt
TinyInt
Bit

14. Numeric Precision (cont.)
Uncomment each pair of SET/SELECT statements and see results
DECLARE
@SmallIntOne SmallInt,
@SmallIntTwo SmallInt,
@SmallIntResultOne SmallInt,
@IntResultOne Int
= 1000
= 1000
= AS int)

15. Numeric Data Types in SQL Server 2000 (cont.)
Identity attributes
int and bigint attributes can be identity attributes
The field’s value for the first record will be automatically set to the identity seed value
I usually set to 1,000 (int) or 10,000 (bigint)
Each new record will get a new value incremented by the identity increment
Almost always one
Widely used for PKs
Foreign Keys will be the same data type but will not be an identity attribute

16. Numeric Data Types (cont.)
BigInt ± 9,223,372,036,854,775,808
Int ± 2,147,483,648
SmallInt ± 32,768
TinyInt (positive only)
Decimal ± 10^38
Money ± 922,337,203,685,
SmallMoney +/- 214,

17. Date Data Types in SQL Server 2000
datetime
January 1, 1753 to December 31, 9999
Accurate to 3 hundredths of a second
smalldatetime
January 1, 1900 to June 6, 2079
Accurate to one minute
Remember the year 2000 problem
Required time precision (rather than maximum date allowed) may determine datatype chosen
Use “___Date” or “___Time” in naming to indicate stored precision

18. Text Data Types in SQL Server 2000
Unicode vs. nonUnicode
Unicode allows the extended character set needed to represent many foreign, especially Oriental, languages
Unicode uses two bytes per character
nonUnicode limited to 255 characters and supports most European languages
Text/character fields are specified with their maximum length

19. Text Data Types in SQL Server 2000
char(n) up to 8,000 characters
Fixed length text field n characters long
Shorter values will be padded with spaces
Wasted space but efficient processing
May require trimming when retrieving
varchar(n) up to 8,000 characters
variable length text field n characters long
text(n) up to 2,147,483,647 characters
Variable length text field allows for large text fields
May not be searched with SQL comparisons

20. Text Data Types in SQL Server 2000 (cont.)
nchar(n), nvarchar, ntext are Unicode versions of char, varchar, and text data types
Don’t be stingy declaring text fields but don’t be wasteful, either
char data types can blow up database size quickly
varchar and text fields can require additional processing
Avoid searching within long text values unless necessary

21. Other Data Types in SQL Server 2000
binary, varbinary, and image are three different data types that store binary values
images
formatted documents such as Excel or Word documents
Avoid storing binary data in the database
uniqueidentifier is a field that automatically creates a value guaranteed to be unique anywhere in the world
See text for info on cursor, rowversion, and sql_variant
Don’t even think about using sql_variant for normal business data design

22. Data Type Considerations
The attribute data types are also the same datatypes available for use in stored procedures
Parameters
Variables
Ensure that variable/parameter data type is consistent with its use
Will hold required value
Is consistent with field datatypes with which it is compared
DECLARE
@SmallIntOne SmallInt,
@SmallIntTwo SmallInt,
@SmallIntResultOne SmallInt,
@IntResultOne Int

23. Domain Constraints
Domain constraints are critical limitations on the values that attributes can take on
Is a value required?
Always for PK attributes
What about other attributes?
Is value numeric, textual, boolean, date?
Are there ranges the value must be in or must not be in?
Are there limited choices for the value (e.g., subtype identifier codes, state abbreviations)
Other examples

24. Domain Constraints (cont.)
Some domain constraints are simple
Last names may not be null and must be alphabetic characters between two and 30 characters in length
Some domain constraints can be more complex
Social security numbers will be recorded as character strings with three numeric characters, a dash, two numeric characters, a dash, and four numeric characters and will be exactly eleven characters long

25. Domain Constraints (cont.)
Many domain constraints contain ranges
Minimum or maximum values
Numbers
Dates
Price must be greater than zero and less than 10,000
Membership date must be after 6/6/55
Domain constraints may specify a default value
Quantity defaults to 1
Purchase date defaults to current date

26. Domain Constraints (cont.)
Some domain constraints can be expressed in terms of calculated values when calculations refer to system values
Birth date must be more than 21 years earlier than today
More complex calculations to enforce business rules are implemented as operational constraints (triggers)
Inventory quantity on hand is the sum of all items received less the sum of all items sold less the sum of all inventory adjustments
Covered in the next lesson

27. Domain Constraints
Identifier Attributes (Primary Keys) will have special domain constraints
Cannot be null
Single attribute identifiers must be unique
Composite identifiers must be unique (though each component attribute will not be)
Some other attributes or sets of attributes may also be set to be unique
SSN and driver's license number in the same entity
Use an Index required to be unique to implement

28. Domain Constraints (cont.)
Two ways to implement domain constraints
Specify each aspect of the domain for each attribute
Specify named domains (rules)
A "Last Name" domain may have all the rules for last name attributes
Different entities with last name attributes would use the named domain for those attributes E.g., Salesrep, Employee, Customer, Supplier
DBMS must support named domains (called rules in SQL Server)
Bind rule to a column