SQL Server requires that each variable and column in a table should be defined with respect to the type of data it will store. From a bit to a huge image and binary storage types, the allocation is supposed to help the user conform to the data required, and help the engine allocate space and processing speed efficiently.



Built-in data types

SQL Server 2000 recognizes the following built in data types:

Data Types

Description

bigint

Integer data from -2^63 through 2^63-1

int

Integer data from -2^31 through 2^31 - 1

smallint

Integer data from -2^15 through 2^15 - 1

tinyint

Integer data from 0 through 255

bit

Integer data with either a 1 or 0 value

decimal

Fixed precision and scale numeric data from -10^38 +1 through 10^38 -1

numeric

Fixed precision and scale numeric data from -10^38 +1 through 10^38 -1

money

Monetary data values from -2^63 through 2^63 - 1

smallmoney

Monetary data values from -214,748.3648 through +214,748.3647

float

Floating precision number data from -1.79E + 308 through 1.79E + 308

real

Floating precision number data from -3.40E + 38 through 3.40E + 38

datetime

Date and time data from January 1, 1753, through December 31, 9999,

with an accuracy of 3.33 milliseconds

smalldatetime

Date and time data from January 1, 1900, through June 6, 2079,

with an accuracy of one minute

char

Fixed-length character data with a maximum length of 8,000 characters

varchar

Variable-length data with a maximum of 8,000 characters

text

Variable-length data with a maximum length of 2^31 - 1 characters

nchar

Fixed-length Unicode data with a maximum length of 4,000 characters

nvarchar

Variable-length Unicode data with a maximum length of 4,000 characters

ntext

Variable-length Unicode data with a maximum length of 2^30 - 1 characters

binary

Fixed-length binary data with a maximum length of 8,000 bytes

varbinary

Variable-length binary data with a maximum length of 8,000 bytes

image

Variable-length binary data with a maximum length of 2^31 - 1 bytes

cursor

A reference to a cursor

sql_variant

A data type that stores values of various data types,

except text, ntext, timestamp, and sql_variant

table

A special data type used to store a result set for later processing

timestamp

A database-wide unique number that gets updated every time

a row gets updated

uniqueidentifier

A globally unique identifier

Bigint, sql_variant, and table are new to SQL Server 2000

User-defined data types

You can make user-defined data types too, which sometimes can be more descriptive of the value types held in the object. This may make it easier for the programmer to document and work with the data. These data types are based on the built in types, and can be outfitted with preprogrammed defaults, checks, constraints, etc. . To create a user-defined data type, use

sp_addtype datatypename, basedatatype, ‘NULL'/'NOT NULL'



How to choose the appropriate data type

SQL Server stores data in data pages that are 8Kb (8192 bytes) in size. The system uses some of that s Sometimes, the system uses only 8060 bytes are availableto that are available to store user's data. Consider the size of a row of data in your tables. If the rows are large, make sure that multiples of the fit conveniently on a data page so that page space is not wasted. This is cut down on disk paging overhead when accessing the data. You want to maximize the number of rows of data which that will fit on a page. This can be accomplished both by splitting the tables, and by choosing the smallest data type which that will accommodate your data. .

In you are using integer data, data; consider that the tinyint datatype will accommodate data which that will fit into one byte of storage. So if the range of all of the data in your field (or variable) is between 0 and 255, use the tinyint datatype. If the range is between -32,768 and 32,767, use the smallint data type. And if If you need to store integer data from -2,147,483,648 through 2,147,483,647, use int data type.

Similarly with smallmoney. If smallmoney. if your value range is between -214748.3648 and 214,748.3647, use the smallmoney datatype.

Use smalldatetime data type instead of datetime data type, if you need to store the date and time data from January 1, 1900 through June 6, 2079, with accuracy to the minute.

Prefer varchar.nvarchar to text/ntext whenever possible because the text and image fields are stored separately, which produces additional paging. And prefer char/varchar to nchar/nvarchar data types because the n types require twice as much storage space. The n types are used primarily for unicode data.



Resources

• Tutorial: SQL 7 & Database Files

This is a useful tutorial on SQL & and database Files.

• Information: Complete information on SQL

This resource provides complete information on SQL.

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