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SQL - Data Types

SQL data type is an attribute that specifies type of data of any object. Each column, variable and expression has related data type in SQL.
You would use these data types while creating your tables. You would choose a particular data type for a table column based on your requirement.
SQL Server offers six categories of data types for your use:

Exact Numeric Data Types:

decimal-10^38 +110^38 -1
numeric-10^38 +110^38 -1

Approximate Numeric Data Types:

float-1.79E + 3081.79E + 308
real-3.40E + 383.40E + 38

Date and Time Data Types:

datetimeJan 1, 1753Dec 31, 9999
smalldatetimeJan 1, 1900Jun 6, 2079
dateStores a date like June 30, 1991
timeStores a time of day like 12:30 P.M.
Note: Here, datetime has 3.33 milliseconds accuracy where as smalldatetime has 1 minute accuracy.

Character Strings Data Types:

charcharMaximum length of 8,000 characters.( Fixed length non-Unicode characters)
varcharvarcharMaximum of 8,000 characters.(Variable-length non-Unicode data).
varchar(max)varchar(max)Maximum length of 231characters, Variable-length non-Unicode data (SQL Server 2005 only).
texttextVariable-length non-Unicode data with a maximum length of 2,147,483,647 characters.

Unicode Character Strings Data Types:

DATA TYPEDescription
ncharMaximum length of 4,000 characters.( Fixed length Unicode)
nvarcharMaximum length of 4,000 characters.(Variable length Unicode)
nvarchar(max)Maximum length of 231characters (SQL Server 2005 only).( Variable length Unicode)
ntextMaximum length of 1,073,741,823 characters. ( Variable length Unicode )

Binary Data Types:

DATA TYPEDescription
binaryMaximum length of 8,000 bytes(Fixed-length binary data )
varbinaryMaximum length of 8,000 bytes.(Variable length binary data)
varbinary(max)Maximum length of 231 bytes (SQL Server 2005 only). ( Variable length Binary data)
imageMaximum length of 2,147,483,647 bytes. ( Variable length Binary Data)

Misc Data Types:

DATA TYPEDescription
sql_variantStores values of various SQL Server-supported data types, except text, ntext, and timestamp.
timestampStores a database-wide unique number that gets updated every time a row gets updated
uniqueidentifierStores a globally unique identifier (GUID)
xmlStores XML data. You can store xml instances in a column or a variable (SQL Server 2005 only).
cursorReference to a cursor object
tableStores a result set for later processing