Sequence Project Showplan Operator 序列映射运算符
文章：https://www.cnblogs.com/lyhabc/articles/3960373.html
上面文章也有解释
序列映射运算符会从一个已经排序的集合里通过不停添加集合里的列执行计算。
运算符根据一个或多个列的值把输入集合分为多个片段。然后运算符一次输出一个片段。
这些列在序列投影运算符里会被显示为参数。
SQL Server支持四种类型排序函数：RANK, DENSE_RANK, ROW_NUMBER, NTILE
序列投影会生成有（一个序列映射）和（两个片段）的执行计划
The Sequence Project operator adds columns to perform computations over an ordered set. It divides the input set into segments based on the value of one or more columns. The operator then outputs one segment at a time. These columns are shown as arguments in the Sequence Project operator.
Microsoft SQL Server supports four types of functions: RANK, DENSE_RANK, ROW_NUMBER, and NTILE. Sequence Projectwill generate plans that have a Sequence Project and generally two segments.
Sequence Project is a physical and a logical operator.
https://msdn.microsoft.com/en-us/library/ms187041(v=sql.105).aspx