Each table column in a database must be associated with
a data type. This enables the database to store and
manage the data efficiently. A data type is an attribute
that specifies the type of data that the column can
store.
Most commercial databases nowadays provide 2 types of
data types - system data types and user-defined data
types. System data types are commonly used data types
that are defined by the database vendor. These system
data types tend to be the same across most types of
database. User-defined data types on the other hand,
are defined by the user. User-defined data types are
only used when the system data types are not sufficient
or will cause inefficiency.
The following are some of the more common system data
types:
Binary Varying
Variable-length binary data with a maximum length
of 8,000 bytes
Char Varying
Variable-length non-Unicode data with a maximum
of 8,000 characters
Character
Fixed-length non-Unicode character data with a
maximum length of 8,000 characters
Dec
Fixed precision and scale numeric data from -10^38
+1 through 10^38 –1
Double Precision
Floating precision number data with the following
valid values:
-1.79E + 308 through -2.23E - 308, 0 and 2.23E
+ 308 through 1.79E + 308
Integer
Integer (whole number) data from -2^31 (-2,147,483,648)
through 2^31 - 1 (2,147,483,647)
National
Character
Fixed-length Unicode data with a maximum length
of 4,000 characters.
National
Character Varying
Variable-length Unicode data with a maximum length
of 4,000 characters
RowVersion or
TimeStamp
A database-wide unique number that gets updated
every time a row gets updated
DateTime
Date and time data from January 1, 1753, through
December 31, 9999, with an accuracy of three-hundredths
of a second, or 3.33 milliseconds
(the above are excerpted from SQL Server documentation)
Each database vendor would have their own system data
types but the common ones (see above) tend to be very
similar with the data types defined by the ANSI-ISO
SQL 92 standards. However, it would still be wise to
test any database application out with the different
database types to qualify the database application for
each database type.
