Using the Get* Methods to Read Column Values Before I show you the other Get* methods that read column values, you need to know the standard C# types and the values they support.. You ne
Trang 1Using the Get* Methods to Read Column Values
Before I show you the other Get* methods that read column values, you need to know the standard C# types and the values they support You need to know these so that you can understand the type compatibilities between C# and SQL Server shown later Table 9.3
shows the standard C# types, along with the underlying NET type and the values that can
be stored in the C# type
Table 9.3: STANDARD C# AND NET TYPES
C#
TYPE
.NET
TYPE
VALUES
bool Boolean A Boolean true or false value
byte Byte An 8-bit unsigned integer between 0 and 28 - 1(255)
char Char A 16-bit Unicode character
DateTime DateTime A date and time between 12:00:00 AM January 1, 0001 and
11:59:59 PM December 31, 9999
decimal Decimal A fixed precision and scale number between approximately +/-1.0
*10-28 and approximately +/-7.9 *1028 with 28 significant figures
of precision
double Double A 64-bit floating-point number between approximately +/-5 *10
-324
and approximately +/-1.7 *10308 with 15 to 16 significant figures of precision
float Single A 32-bit floating-point number between approximately +/-1.5 *10
-45
to approximately +/-3.4 *1038 with 7 significant figures of precision
Guid Guid A 128-bit unsigned integer value (16 bytes) that that is unique
across all computers and networks
int Int32 A 32-bit signed integer between -231 (-2,147,483,648) and 231 - 1
(2,147,483,647)
long Int64 A 64-bit signed integer between -263
(-9,223,372,036,854,775,808) and 263 - 1 (9,223,372,036,854,775,807)
sbyte SByte An 8-bit signed integer between -27 (-128) and 27 - 1 (127)
short Int16 A 16-bit signed integer between -215 (-32,768) and 215 - 1
(32,767)
string String A variable-length string of 16-bit Unicode characters
Trang 2Table 9.3: STANDARD C# AND NET TYPES
C#
TYPE
.NET
TYPE
VALUES
uint UInt32 A 32-bit unsigned integer between 0 and 232 - 1 (4,294,967,295) ulong UInt64 A 64-bit unsigned integer between 0 and 264 - 1
(18,446,744,073,709,551,615)
ushort UInt16 A 16-bit unsigned integer between 0 and 216 - 1 (65,535)
Note The standard C# types are defined in the System namespace.
DataReader Get* methods that return each C# type You use this table to figure out which method to call to get a specific column type For example, if you need to get the value of
a bigint column, you call the GetInt64() method that returns a long
Table 9.4: SQL SERVER TYPES, COMPATIBLE STANDARD C# TYPES, AND
GET* METHODS
SQL SERVER TYPE COMPATIBLE STANDARD C# TYPE GET* METHOD
Trang 3Table 9.4: SQL SERVER TYPES, COMPATIBLE STANDARD C# TYPES, AND
GET* METHODS
SQL SERVER TYPE COMPATIBLE STANDARD C# TYPE GET* METHOD
Note You can see the SQL Server types and the values supported by those types in Table
Note The Get* methods are defined in all of the DataReader classes and work for all
databases
Next you'll see how to use some of the methods shown in Table 9.4