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语法：<主字符串>.Substring(<起始字符位置>, <字符长度>)
说明：从主字符串中返回一个子字符串，子字符串从指定的字符位置开始且具有指定的长度。
示例：{Description.Substring(1, 10)}
比如，我们可以使用 SubString 函数嵌套Ceiling函数实现以下动态显示订单数量所属星标级别的效果。
接下来为您介绍具体的实现过程。
1. 新建报表，使用表格组件并绑定数据字段。
2. 使用ToString函数示例将“ 订购日期 ”改为：{ Fields!订购日期.Value.ToString( "yyyy-MM-dd")} ，使其仅显示年月日。
3. 在右侧增加一列，表头单元格输入“ 星标级别 ”，数据单元格输入表达式： {"★★★★★".SubString(5 - Ceiling(Fields!购买数量.Value / 4))} 。
4. 预览报表，可见最后一列的星标会根据购买数量的级别进行动态显示。如本文开篇所示。