简谈SQL Server主键和自动编号
除了使用存储过程实现COMB数据外，我们也可以使用C#生成COMB数据，这样所有主键生成工作可以在客户端完成。C#代码如下：
//================================================================
/**////
/// 返回 GUID 用于数据库操作，特定的时间代码可以提高检索效率
///
/// COMB (GUID 与时间混合型) 类型 GUID 数据
public static Guid NewComb()
{
byte[] guidArray = System.Guid.NewGuid().ToByteArray();
DateTime baseDate = new DateTime(1900,1,1);
DateTime now = DateTime.Now;
// Get the days and milliseconds which will be used to build the byte string TimeSpan days = new TimeSpan(now.Ticks - baseDate.Ticks);
TimeSpan msecs = new TimeSpan(now.Ticks - (new DateTime(now.Year, now.Month, now.Day).Ticks));
// Convert to a byte array
// Note that SQL Server is accurate to 1/300th of a millisecond so we divide by 3.333333
byte[] daysArray = BitConverter.GetBytes(days.Days);
byte[] msecsArray = BitConverter.GetBytes((long)(msecs.TotalMilliseconds/3.333333));
// Reverse the bytes to match SQL Servers ordering Array.Reverse(daysArray);
Array.Reverse(msecsArray);
// Copy the bytes into the guid Array.Copy(daysArray, days
Array.Length - 2, guidArray, guidArray.Length - 6, 2);
Array.Copy(msecsArray, msecsArray.Length - 4, guidArray, guidArray.Length - 4, 4);
return new System.Guid(guidArray); }
//================================================================
/**////
/// 从 SQL SERVER 返回的 GUID 中生成时间信息
///
///
包含时间信息的 COMB
/// 时间
public static DateTime GetDateFromComb
(System.Guid guid)
{
DateTime baseDate = new DateTime(1900,1,1);
byte[] daysArray = new byte[4];
byte[] msecsArray = new byte[4];
byte[] guidArray = guid.ToByteArray();
// Copy the date parts of the guid to the respective byte arrays.
Array.Copy(guidArray, guidArray.Length - 6, daysArray, 2, 2);
Array.Copy(guidArray, guidArray.Length - 4, msecsArray, 0, 4);
// Reverse the arrays to put them into the appropriate order
Array.Reverse(daysArray);
Array.Reverse(msecsArray);
// Convert the bytes to ints int
days = BitConverter.ToInt32(daysArray, 0);
int msecs = BitConverter.ToInt32(msecsArray, 0);
DateTime date = baseDate.AddDays(days);
date = date.AddMilliseconds(msecs * 3.333333);
return date;
}
/**////
/// 返回 GUID 用于数据库操作，特定的时间代码可以提高检索效率
///
/// COMB (GUID 与时间混合型) 类型 GUID 数据
public static Guid NewComb()
{
byte[] guidArray = System.Guid.NewGuid().ToByteArray();
DateTime baseDate = new DateTime(1900,1,1);
DateTime now = DateTime.Now;
// Get the days and milliseconds which will be used to build the byte string TimeSpan days = new TimeSpan(now.Ticks - baseDate.Ticks);
TimeSpan msecs = new TimeSpan(now.Ticks - (new DateTime(now.Year, now.Month, now.Day).Ticks));
// Convert to a byte array
// Note that SQL Server is accurate to 1/300th of a millisecond so we divide by 3.333333
byte[] daysArray = BitConverter.GetBytes(days.Days);
byte[] msecsArray = BitConverter.GetBytes((long)(msecs.TotalMilliseconds/3.333333));
// Reverse the bytes to match SQL Servers ordering Array.Reverse(daysArray);
Array.Reverse(msecsArray);
// Copy the bytes into the guid Array.Copy(daysArray, days
Array.Length - 2, guidArray, guidArray.Length - 6, 2);
Array.Copy(msecsArray, msecsArray.Length - 4, guidArray, guidArray.Length - 4, 4);
return new System.Guid(guidArray); }
//================================================================
/**////
/// 从 SQL SERVER 返回的 GUID 中生成时间信息
///
///
包含时间信息的 COMB
/// 时间
public static DateTime GetDateFromComb
(System.Guid guid)
{
DateTime baseDate = new DateTime(1900,1,1);
byte[] daysArray = new byte[4];
byte[] msecsArray = new byte[4];
byte[] guidArray = guid.ToByteArray();
// Copy the date parts of the guid to the respective byte arrays.
Array.Copy(guidArray, guidArray.Length - 6, daysArray, 2, 2);
Array.Copy(guidArray, guidArray.Length - 4, msecsArray, 0, 4);
// Reverse the arrays to put them into the appropriate order
Array.Reverse(daysArray);
Array.Reverse(msecsArray);
// Convert the bytes to ints int
days = BitConverter.ToInt32(daysArray, 0);
int msecs = BitConverter.ToInt32(msecsArray, 0);
DateTime date = baseDate.AddDays(days);
date = date.AddMilliseconds(msecs * 3.333333);
return date;
}
结语
数据库主键在数据库中占有重要地位。主键的选取策略决定了系统是否高效、易用。本文比较了四种主键选取策略的优缺点，并提供了相应的代码解决方案，希望对大家有所帮助。
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