序列顶部函数

概述

以下 C API 函数接受各种输入序列参数，并生成结果序列或标量类型，具体描述见下表：

函数	说明
seq_top_max(n)	返回整数序列中的前 n 个最大值
seq_top_min(n)	返回整数序列中的前 n 个最小值
seq_top_pos_max(n)	返回整数序列中前 n 个最大值的位置
seq_top_pos_min(n)	返回整数序列中前 n 个最小值的位置

seq_top_max() 函数返回输入序列中的最大 N 个值（在此示例中为 3 个）。seq_top_min() 函数返回最小的 N 个值。seq_top_pos_max() 函数返回输入序列中最大 N 个值的位置。seq_top_pos_min() 函数返回输入序列中最小 N 个值的位置。

以下是一个展示这些功能的示例脚本：

    create table SimpleSequence( testNumber unsigned(4) primary key,
    dVal1 sequence(double), dVal2 sequence(double) );
    INSERT INTO SimpleSequence(testNumber,dVal1,dVal2)
    VALUES(1,[1,2,3,4,5,6,7,8,9], [1,2,3,4,5,6,7,8,9]);
     
    SELECT dVal1, dVal2, seq_top_max(dVal1,3) as "top_max",
        seq_top_pos_max(dVal1,3) as "top_pos_max",
        seq_top_min(dVal2,3) as "top_min",
        seq_top_pos_min(dVal2,3) as "top_pos_min"
    FROM SimpleSequence WHERE testNumber=1;
     
    dVal1{}
    dVal2{}
    top_max{}
    top_pos_max{}
    top_min{}
    top_pos_min{}
    ------------------------------------------------------------------------------
    {1.000000, 2.000000, 3.000000, 4.000000, 5.000000, 6.000000, 7.000000,
      8.000000, 9.000000}
    {1.000000, 2.000000, 3.000000, 4.000000, 5.000000, 6.000000, 7.000000,
      8.000000, 9.000000}
    {9.000000, 8.000000, 7.000000}
    {8, 7, 6}
    {1.000000, 2.000000, 3.000000}
    {0, 1, 2}

可以在 samples/xsql/scripts/financial 目录中使用以下命令运行此 select 语句的示例脚本：

    g 11

示例

以下是一个示例代码片段，展示了这些函数的用法：

    -- _top_max, _top_min, _top_pos_max, _top_pos_min
            
    CREATE TABLE SimpleSequence11( testNumber unsigned(4) primary key,
        dVal1 sequence(double), dVal2 sequence(double) );
    INSERT INTO SimpleSequence11(testNumber,dVal1,dVal2)
        VALUES(1,[1,2,3,4,5,6,7,8,9], [1,2,3,4,5,6,7,8,9]);
 
    SELECT dVal1, dVal2, seq_top_max(dVal1,3) as "top_max",
        seq_top_pos_max(dVal1,3) as "top_pos_max",
        seq_top_min(dVal2,3) as "top_min",
        seq_top_pos_min(dVal2,3) as "top_pos_min"
    FROM SimpleSequence11 WHERE testNumber=1;
     
    dVal1{} 
      dVal2{}  
     top_max{} 
    top_pos_max{} 
        top_min{} 
    top_pos_min{}
    -------------------------------------------------------------------------
    {1, 2, 3, 4, 5, 6, 7, 8, 9} 
        {1, 2, 3, 4, 5, 6, 7, 8, 9} 
        {9, 8, 7}       
    {8, 7, 6}       
    {1, 2, 3} 
          {0, 1, 2}