/// <summary>
/// 对命令文本进行分段处理，使之能够返回小范围内的数据。
/// </summary>
/// <param name="commandText">命令文本。</param>
/// <param name="segment">数据分段对象。</param>
/// <returns>处理后的分段命令文本。</returns>
/// <exception cref="SegmentNotSupportedException">当前数据库或版本不支持分段时，引发该异常。</exception>
public virtual string Segment(string commandText, IDataSegment segment)
{
var orderBy = DbUtility.FindOrderBy(commandText);
var regAlias = new Regex(@"(\w+)?\.");
//如果有排序
if (!string.IsNullOrEmpty(orderBy))
{
//去除子句中的Order并移到OVER后
commandText = string.Format(@"
SELECT T.* FROM
(
SELECT T.*, ROW_NUMBER() OVER ({2}) AS ROW_NUM
FROM ({0}) T
) T
WHERE {1}",
commandText.Replace(orderBy, string.Empty).Trim(),
segment.Condition("ROW_NUM"),
regAlias.Replace(orderBy, string.Empty));
}
else
{
commandText = string.Format(@"
SELECT T.* FROM
(
SELECT T.*, ROW_NUMBER() OVER (ORDER BY (SELECT 1)) AS ROW_NUM
FROM ({0}) T
) T
WHERE {1}",
commandText, segment.Condition("ROW_NUM"));
}
return(commandText);
}
/// <summary>
/// 对命令文本进行分段处理，使之能够返回小范围内的数据。
/// </summary>
/// <param name="commandText">命令文本。</param>
/// <param name="segment">数据分段对象。</param>
/// <returns>处理后的分段命令文本。</returns>
/// <exception cref="SegmentNotSupportedException">当前数据库或版本不支持分段时，引发该异常。</exception>
public virtual string Segment(string commandText, IDataSegment segment)
{
var regxOrder = new Regex(@"order\s+by ([\W|\w])+", RegexOptions.IgnoreCase);
var regAlias = new Regex(@"(\S+)?\.");
//如果有排序
if (regxOrder.IsMatch(commandText))
{
var matchs = regxOrder.Matches(commandText);
//去除子句中的Order并移到OVER后
commandText = string.Format(@"
SELECT T.* FROM
(
SELECT T.*, ROW_NUMBER() OVER ({2}) AS ROW_NUM
FROM ({0}) T
) T
WHERE {1}",
regxOrder.Replace(commandText, "").Trim(),
segment.Condition("ROW_NUM"),
regAlias.Replace(matchs[matchs.Count - 1].Value, ""));
}
else
{
commandText = string.Format(@"
SELECT T.* FROM
(
SELECT T.*, ROW_NUMBER() OVER (ORDER BY (SELECT 1)) AS ROW_NUM
FROM ({0}) T
) T
WHERE {1}",
commandText, segment.Condition("ROW_NUM"));
}
return(commandText);
}
