asp.net下SQLite(轻量级最佳数据库) 原理分析和开发应用(2)-木庄网络博客

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SQLite 分页查询

写法1:

SELECT * FROM TABLE1 LIMIT 20 OFFSET 20 ;

写法2:

SELECT * FROM TABLE1 LIMIT 20 , 20;

SQLite 文件的压缩
在多次删除数据、插入数据、更新数据后，数据库体积增大，但实际有效数据量很小，则需要对数据库进行压缩、整理，把已经删除的数据从物理文件中移除。调用一下SQL命令即可：

VACUUM

VACUUM的实现

数据插入与更新

使用REPLACE替代INSERT、UPDATE命令。在无满足条件记录，则执行Insert，有满足条件记录，则执行UPDATE。

代码如下:

REPLACE INTO TABLE1(col1, col2, col3) VALUES(val1, val2,val3);

Insert or Replace Into 和Replace Into 的效果是一样的上面这句话也可以这样写

代码如下:

Insert or Replace INTO TABLE1(col1, col2, col3) VALUES(val1, val2,val3);

字符编码转换
sqlite3的源码中，提供了utf8ToUnicode()、unicodeToUtf8()、mbcsToUnicode()、unicodeToMbcs()、sqlite3_win32_mbcs_to_utf8 ()、utf8ToMbcs ()等8个函数进行字符在不同编码间的转换，但未在sqlite3.def、sqlite3.h文件中列出，即未对外公开。这些函数中，都使用了MultiByteToWideChar()、WideCharToMultiByte()两个函数实现字符间转换。
开发示例

代码如下:

using System;
using System.Data;
using System.Data.SQLite;
using System.Collections.Generic;
using System.IO;
namespace FileSystemWatcthrDemo.DataHelper
{
public class SqLiteHelper
{
/// <summary>
/// ConnectionString样例：Datasource=Test.db3;Pooling=true;FailIfMissing=false
/// </summary>
public static string ConnectionString
{
get
{
return @"Data source= "+DataBasePath+";";
}
set { throw new NotImplementedException(); }
}
public static string DataBasePath
{
get { return "SpringYang.db";};
}
private static object lockObject = new object();
private static void PrepareCommand(SQLiteCommand cmd, SQLiteConnection conn, string cmdText, List<SQLiteParameter> parameters)
{
if (conn.State != ConnectionState.Open)
conn.Open();
cmd.Parameters.Clear();
cmd.Connection = conn;
cmd.CommandText = cmdText;
cmd.CommandType = CommandType.Text;
cmd.CommandTimeout = 30;
foreach (var parameter in parameters)
{
cmd.Parameters.Add(parameter);
}
}
public static DataSet ExecuteQuery(string cmdText, List<SQLiteParameter> parameters)
{
lock (lockObject)
{
using (SQLiteConnection conn = new SQLiteConnection(ConnectionString))
{
using (SQLiteCommand command = new SQLiteCommand())
{
DataSet ds = new DataSet();
PrepareCommand(command, conn, cmdText, parameters);
SQLiteDataAdapter da = new SQLiteDataAdapter(command);
da.Fill(ds);
return ds;
}
}
}
}
public static int ExecuteNonQuery(string cmdText, List<SQLiteParameter> parameters)
{
lock (lockObject)
{
using (SQLiteConnection conn = new SQLiteConnection(ConnectionString))
{
using (SQLiteCommand command = new SQLiteCommand())
{
PrepareCommand(command, conn, cmdText, parameters);
return command.ExecuteNonQuery();
}
}
}
}
public static SQLiteDataReader ExecuteReader(string cmdText, List<SQLiteParameter> parameters)
{
lock (lockObject)
{
SQLiteConnection conn = new SQLiteConnection(ConnectionString);
SQLiteCommand command = new SQLiteCommand();
PrepareCommand(command, conn, cmdText, parameters);
SQLiteDataReader sqLiteDataReader = command.ExecuteReader();
return sqLiteDataReader;
}
}
public static object ExecuteScalar(string cmdText, List<SQLiteParameter> parameters)
{
lock (lockObject)
{
using (SQLiteConnection conn = new SQLiteConnection(ConnectionString))
{
using (SQLiteCommand command = new SQLiteCommand())
{
PrepareCommand(command, conn, cmdText, parameters);
return command.ExecuteScalar();
}
}
}
}
public static void CreateDataBase()
{
if (!File.Exists(DataBasePath))
SQLiteConnection.CreateFile(DataBasePath);
CreateTable();
}
public static void CreateTable()
{
ExecuteNonQuery(CodeDetailTabale, null);
}
private static string CodeDetailTabale
{
get
{
return @"CREATE TABLE [CodeDetail] (
[CdType] [nvarchar] (10) NOT NULL ,
[CdCode] [nvarchar] (20) NOT NULL ,
[CdString1] [ntext] NOT NULL ,
[CdString2] [ntext] NOT NULL ,
[CdString3] [ntext] NOT NULL,
PRIMARY KEY (CdType,CdCode)
) ;";
}
}
}
}

示例讲解
A、使用到自己定义的锁private static object lockObject = new object();
B、使用完连接后都进行关闭操作。使用了using
C、创建数据库命令：SQLiteConnection.CreateFile(DataBasePath);
最后再讲解个Insert or Replace into的经典用法

代码如下:

Insert or Replace INTO User(ID, Name,Age) Select old.ID,new.Name,new.Age From
(select 'Spring Yang' as Name, '25' as Age) as new left join (Select ID,Name from User where Name = 'Spring Yang' ) as old on old.Name = new.Name

标签：SQLite

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