Introduction To SQLUnit 5

Modern Business Technology

Introduction To TSQLUnit 5

Developed by

Michael Hotek

Naming Tables

• Up to 30 characters• No blanks• Underscore is permitted• Must be unique within the database• Keep abbreviations to a minimum• Names should reflect the contents of

the table

Naming Columns

• Up to 30 characters• No blanks• Underscore is permitted• Must be unique within the table• Keep abbreviations to a minimum• Names should reflect the contents of

the column• Names should be readily

recognizable

Datatype Considerations

• Determine what type of data will be stored

• Find the range of possible values• Determine the accuracy of numeric

columns• Efficiency• Utilize user defined datatypes to

enforce consistency

Datatypes

• Exact Numeric– Stores data with a specific accuracy

• Approximate numeric– Stores data with accuracy dependent

upon calculations performed

• Money– Monetary data

• Date and time– Storage of dates and times

• Character– Alphanumeric data

• Binary– Images, byte and bit values

Exact Numeric

• tinyint– Whole numbers between 0 and 255– 1 byte of storage

• smallint– Whole numbers between -32678 and

32677– 2 bytes of storage

• numeric(p,s)– Decimals between -1038 and 1038-1– 2 to 17 bytes

• decimal(p,s)– Decimals between -1038 and 1038-1– 2 to 17 bytes

• s = number of digits to the right of the decimal

• p = total number of digits

Approximate Numeric

• Float(p)– Floating point numbers– 4 or 8 bytes of storage

• double precision– floating point numbers– 8 bytes of storage

• real– floating point numbers– 4 bytes of storage

• During arithmetic operations, the number of digits to the right of a decimal point will round based upon the values in the calculation

• Float allows you to specific the precision, but not the location of the significant digits in relation to the decimal point

Money

• money– -922,337,203,685,477.5808 to

922,337,203,685,477.5807– 8 bytes of storage

• smallmoney– -214,748.3648 to 214,748.3647– 4 bytes of storage

• Accurate up to 4 decimal places, but are rounded to 2 places when displaying

Datetime

• datetime– 1/1/1753 to 1/31/9999

– 8 bytes of storage

• smalldatetime– 1/1/1900 to 6/6/2079

– 4 bytes of storage

• There is no separate datatype for just times

• Time is stored along with a date with an accuracy of 1/300th of a second

• Due to the limitation on the range of data, a smalldatetime should no longer be used.

• Dates and times can be entered into these columns using a wide variety of date and time formats

• The default display type is determined from the default language for the server

Character

• char(n) and nchar(n)– Fixed length alphanumeric data– n bytes of storage

• varchar(n) and nvarchar(n)– Variable length alphanumeric data– actual length of data

• text– Unbounded alphanumeric data– 16 bytes for an address + multiples of 2K

• Char datatypes provide a small performance benefit over varchar.

• If the data size is predictable or 8 characters or less, use a char

• nchar and nvarchar are used to store multi-byte characters such as Chinese and Japanese

Binary

• Bit– 0 or 1– 1 byte of storage

• binary(n)– up to 255 bytes– n bytes of storage

• varbinary– up to 255 bytes– actual length of data

• image– up to 231-1 bytes– 16 bytes address + multiples of 2K bytes

of storage

Unbound Data

• The text and image datatypes are used to store large amounts of data

• Text is used for alphanumeric data• Image is used for binary data• It is highly recommended that you

avoid this two datatypes if at all possible– They can cause a serious performance

problem as well as a space problem.– Support for them is very limited

(specialized functions are required to manipulate them)

– No application tool can handle binary data streaming directly from a database

User Defined Datatypes

• SQL Server gives you the ability to create your own datatypes– Enforces consistency among columns– Gives a single point to bind a common

rule or default

• Consists of a name, system datatype, and nullability

Creating UDDTs

• You add new types with sp_addtype

exec sp_addtype empid, int not null

• This says to create a new type called empid that is based upon an integer and can not be null

exec sp_addtype tid, char(6), not null

• This is a new type called tid that can contain up to 6 characters and can not be null

• Use sp_droptype and sp_help type to drop and return information about user datatypes

• An identity is a special column property– Assigned a sequential numeric value for

each row that is inserted– They can be of integer or numeric

datatypes, but are only whole numbers– They can not be null– There can only be one identity column

per table– Can not be updated– Data can be explicitly inserted into them

using set identity_insert <table> on• This should only be done in rare

instances

– Normally start at 1, but a seed value can be defined for them

– This is normally a sequential number, but you should not count on this

Identities

Creating Tables

CREATE TABLE [database.[owner].]table_name ({col_name column_properties [constraint [constraint [...constraint]]] | [[,] constraint]} [[,] {next_col_name | next_constraint}...])

• Maximum number of columns per table is 250

• Maximum row size is 1962 bytes• To get information about a table use

sp_help <table_name>

Create Table Example

CREATE TABLE dbo.authors

(au_id id NOT NULL,

au_lname char(40) NOT NULL,

au_fname char(20) NOT NULL,

phone char(12) NULL,

address varchar(40) NULL,

city varchar(20) NULL,

state char(2) NULL,

zip char(5) NULL,

contract bit NOT NULL)

go

Unit 5 Review

• Table names can be up to 30 characters long and must be unique within a database

• Column names can be up to 30 characters and must be unique within a table

• Types of data are: exact numeric, approximate numeric, money, date time, character, and binary

• Use unbound datatypes only when strictly necessary

• User defined datatypes can be created from system datatypes using sp_addtype

• An identity is a special property for a column that automatically provides a value for new rows

• You can create and remove tables using the create table and drop table commands

• You can only have 250 columns in a table• The maximum size of a row is 1962 bytes

Unit 5 Exercises

• Time allotted for exercises is 30 minutes