using System;
using NewLife.Reflection;
using XCode.Exceptions;
namespace XCode.DataAccessLayer
{
/// <summary>MS系列数据库分页算法</summary>
public static class MSPageSplit
{
/// <summary>分页算法</summary>
/// <remarks>
/// builder里面必须含有排序，否则就要通过key指定主键，否则大部分算法不能使用，会导致逻辑数据排序不正确。
/// 其实，一般数据都是按照聚集索引排序，而聚集索引刚好也就是主键。
/// 所以，只要设置的Key顺序跟主键顺序一致，就没有问题。
/// 如果，Key指定了跟主键不一致的顺序，那么查询语句一定要指定同样的排序。
/// </remarks>
/// <param name="builder"></param>
/// <param name="startRowIndex"></param>
/// <param name="maximumRows"></param>
/// <param name="isSql2005"></param>
/// <param name="queryCountCallback">查询总记录数的委托，近供DoubleTop使用</param>
/// <returns></returns>
public static SelectBuilder PageSplit(SelectBuilder builder, Int64 startRowIndex, Int64 maximumRows, Boolean isSql2005, Func<SelectBuilder, Int64> queryCountCallback = null)
{
// 从第一行开始，不需要分页
// 2012.11.08 注释掉首页使用SELECT TOP的方式，此方式在对有重复数据出现的字段排序时，
// 与Row_Number()的规则不一致，导致出现第一、二页排序出现重复记录。
// 具体可百度一下【结合TOP N和Row_Number()分页因Order by排序规则不同引起的bug】
if (startRowIndex <= 0)
{
if (maximumRows < 1)
{
return builder;
}
else if (builder.KeyIsOrderBy)
{
return builder.Clone().Top(maximumRows);
}
}
if (builder.Keys == null || builder.Keys.Length < 1) throw new XCodeException("分页算法要求指定排序列！" + builder.ToString());
// 其实，一般数据都是按照聚集索引排序，而聚集索引刚好也就是主键
// 所以，只要设置的Key顺序跟主键顺序一致，就没有问题
// 如果，Key指定了跟主键不一致的顺序，那么查询语句一定要指定同样的排序
//// 如果不指定排序，只能使用TopNotIn，另外三种都会影响结果的顺序
//if (String.IsNullOrEmpty(builder.OrderBy))
//{
// // 取前面页（经试验Access字符串主键大概在200行以下）并且没有排序的时候，TopNotIn算法应该是最快的
// if (startRowIndex < 200) return TopNotIn(builder, startRowIndex, maximumRows);
//}
if (isSql2005) return RowNumber(builder, startRowIndex, maximumRows);
// 必须有排序，且排序字段必须就是数字主键
if (builder.IsInt && builder.KeyIsOrderBy) return MaxMin(builder, startRowIndex, maximumRows);
if (maximumRows > 0) return DoubleTop(builder, startRowIndex, maximumRows, queryCountCallback);
return TopNotIn(builder, startRowIndex, maximumRows);
}
/// <summary>最经典的NotIn分页，通用但是效率最差。只需指定一个排序列。</summary>
/// <param name="builder">查询生成器</param>
/// <param name="startRowIndex">开始行，0表示第一行</param>
/// <param name="maximumRows">最大返回行数，0表示所有行</param>
/// <returns>分页SQL</returns>
static SelectBuilder TopNotIn(SelectBuilder builder, Int64 startRowIndex, Int64 maximumRows)
{
if (builder.Keys == null || builder.Keys.Length != 1) throw new ArgumentNullException("Key", "TopNotIn分页算法要求指定单一主键列！" + builder.ToString());
// 分页标准 Select (20,10,ID)
// 1，取目标页之前的20行
// 2，排除前20行之后取10行
// Select Top 10 * From Table Where ID Not In(Select Top 20 ID From Table)
// 构建Select Top 20 ID From Table
var builder1 = builder.Clone().Top(startRowIndex, builder.Key);
SelectBuilder builder2 = null;
if (maximumRows < 1)
builder2 = builder.CloneWithGroupBy("XCode_T0");
else
builder2 = builder.Clone().Top(maximumRows);
builder2.AppendWhereAnd("{0} Not In({1})", builder.Key, builder1);
// 结果列处理
builder2.Column = builder.Column;
// 如果结果列包含有“.”，即有形如tab1.id、tab2.name之类的列时设为获取子查询的全部列
if ((!string.IsNullOrEmpty(builder2.Column)) && builder2.Column.Contains("."))
{
builder2.Column = "*";
}
return builder2;
}
/// <summary>双Top分页，因为没有使用not in，性能比NotIn要好。语句必须有排序，不需额外指定排序列</summary>
/// <param name="builder"></param>
/// <param name="startRowIndex"></param>
/// <param name="maximumRows"></param>
/// <param name="queryCountCallback">查询总记录数的委托，近供DoubleTop使用</param>
/// <returns></returns>
static SelectBuilder DoubleTop(SelectBuilder builder, Int64 startRowIndex, Int64 maximumRows, Func<SelectBuilder, Int64> queryCountCallback)
{
if (builder.Keys == null) throw new ArgumentNullException("Key", "DoubleTop分页算法要求指定排序列！" + builder.ToString());
// 采用DoubleTop分页，最后一页可能有问题，需要特殊处理
if (queryCountCallback != null)
{
// 查询总记录数，计算是否最后一页
var count = queryCountCallback(builder);
// 数据不足
if (count <= startRowIndex) return null;
// 刚好相等的就不必处理了
if (startRowIndex + maximumRows > count) maximumRows = count - startRowIndex;
}
// 分页标准 Select (20,10,ID Desc)
// 1，按原始排序取20+10行，此时目标页位于底部
// 2，倒序过来取10行，得到目标页，但是顺序是反的
// 3，再倒序一次
// 显然，原始语句必须有排序，否则无法倒序。另外，也不能处理maximumRows<1的情况
// Select * From (Select Top 10 * From (Select Top 20+10 * From Table Order By ID Desc) Order By ID Asc) Order By ID Desc
// 找到排序，优先采用排序字句来做双Top排序
var orderby = builder.OrderBy ?? builder.KeyOrder;
Boolean[] isdescs = null;
var keys = SelectBuilder.Split(orderby, out isdescs);
// 把排序反过来
var isdescs2 = new Boolean[keys.Length];
for (int i = 0; i < keys.Length; i++)
{
if (isdescs != null && isdescs.Length > i)
isdescs2[i] = !isdescs[i];
else
isdescs2[i] = true;
}
var reversekeyorder = SelectBuilder.Join(keys, isdescs2);
// 构建Select Top 20 * From Table Order By ID Asc
var builder1 = builder.Clone().AppendColumn(keys).Top(startRowIndex + maximumRows);
// 必须加一个排序，否则会被优化掉而导致出错
if (String.IsNullOrEmpty(builder1.OrderBy)) builder1.OrderBy = builder1.KeyOrder;
var builder2 = builder1.AsChild("XCode_T0").Top(maximumRows);
// 要反向排序
builder2.OrderBy = reversekeyorder;
var builder3 = builder2.AsChild("XCode_T1");
// 结果列处理
builder3.Column = builder.Column;
// 如果结果列包含有“.”，即有形如tab1.id、tab2.name之类的列时设为获取子查询的全部列
if ((!string.IsNullOrEmpty(builder3.Column)) && builder3.Column.Contains("."))
{
builder3.Column = "*";
}
// 让结果正向排序
builder3.OrderBy = orderby;
return builder3;
}
/// <summary>按唯一数字最大最小分页，性能很好。必须指定一个数字型排序列。</summary>
/// <param name="builder">查询生成器</param>
/// <param name="startRowIndex">开始行，0表示第一行</param>
/// <param name="maximumRows">最大返回行数，0表示所有行</param>
/// <returns>分页SQL</returns>
static SelectBuilder MaxMin(SelectBuilder builder, Int64 startRowIndex, Int64 maximumRows)
{
if (builder.Keys == null || builder.Keys.Length != 1) throw new ArgumentNullException("Key", "TopNotIn分页算法要求指定单一主键列！" + builder.ToString());
// 分页标准 Select (20,10,ID Desc)
// Select Top 10 * From Table Where ID>(Select max(ID) From (Select Top 20 ID From Table Order By ID) Order By ID Desc) Order By ID Desc
var builder1 = builder.Clone().Top(startRowIndex, builder.Key);
var builder2 = builder1.AsChild("XCode_T0");
builder2.Column = String.Format("{0}({1})", builder.IsDesc ? "Min" : "Max", builder.Key);
SelectBuilder builder3 = null;
if (maximumRows < 1)
builder3 = builder.CloneWithGroupBy("XCode_T1");
else
builder3 = builder.Clone().Top(maximumRows);
// 如果本来有Where字句，加上And，当然，要区分情况按是否有必要加圆括号
builder3.AppendWhereAnd("{0}{1}({2})", builder.Key, builder.IsDesc ? "<" : ">", builder2);
return builder3;
}
/// <summary>RowNumber分页算法</summary>
/// <param name="builder">查询生成器</param>
/// <param name="startRowIndex">开始行，0表示第一行</param>
/// <param name="maximumRows">最大返回行数，0表示所有行</param>
/// <returns></returns>
static SelectBuilder RowNumber(SelectBuilder builder, Int64 startRowIndex, Int64 maximumRows)
{
//if (maximumRows < 1)
// sql = String.Format("Select * From (Select *, row_number() over({2}) as rowNumber From {1}) XCode_Temp_b Where rowNumber>={0}", startRowIndex + 1, sql, orderBy);
//else
// sql = String.Format("Select * From (Select *, row_number() over({3}) as rowNumber From {1}) XCode_Temp_b Where rowNumber Between {0} And {2}", startRowIndex + 1, sql, startRowIndex + maximumRows, orderBy);
// 如果包含分组，则必须作为子查询
var builder1 = builder.CloneWithGroupBy("XCode_T0");
builder1.Column = String.Format("{0}, row_number() over(Order By {1}) as rowNumber", builder.ColumnOrDefault, builder.OrderBy ?? builder.KeyOrder);
var builder2 = builder1.AsChild("XCode_T1");
// 结果列处理
builder2.Column = builder.Column;
// 如果结果列包含有“.”，即有形如tab1.id、tab2.name之类的列时设为获取子查询的全部列
if ((!string.IsNullOrEmpty(builder2.Column)) && builder2.Column.Contains("."))
{
builder2.Column = "*";
}
// row_number()直接影响了排序，这里不再需要
builder2.OrderBy = null;
if (maximumRows < 1)
builder2.Where = String.Format("rowNumber>={0}", startRowIndex + 1);
else
builder2.Where = String.Format("rowNumber Between {0} And {1}", startRowIndex + 1, startRowIndex + maximumRows);
return builder2;
}
static SelectBuilder Top(this SelectBuilder builder, Int64 top, String keyColumn = null)
{
if (!String.IsNullOrEmpty(keyColumn)) builder.Column = keyColumn;
if (String.IsNullOrEmpty(builder.Column)) builder.Column = "*";
builder.Column = String.Format("Top {0} {1}", top, builder.Column);
return builder;
}
}
}
|