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  • oracle first_value,last_valus

    first_value和last_value 是用来去分析函数窗口中对应列的第一个值和最后一个值的函数。

    语法如下:

    first_value(col [ignore NULLS]) over([PARTITION BY col] [ORDER BY sal] [windows])
    last_value(col [ignore NULLS]) over([PARTITION BY col] [ORDER BY sal] [windows])
    --col          : 表示选取的列
    --ignore NULLS :表示忽略空值
    --PARTITION BY :表示分组
    --ORDER BY     :表示排序
    --windows      :表示窗口,默认值是(RANGE UNBOUNDED PRECEDING AND CURRENT ROW)从第一行到当前行
    --windows      :常用值(ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)从第一行到最后一行               

    示例1:

    SELECT first_value(comm ) over() firstval,
           last_value(comm ) over() lastval,
           e.*
      FROM emp e

    结果:

    示例2:

    SELECT first_value(comm ) over(partition by deptno) firstval,
           last_value(comm ) over(partition by deptno) lastval,
           e.*
      FROM emp e

    结果:

    示例3:

    SELECT first_value(comm ) over(partition by deptno order by sal) firstval,
           last_value(comm ) over(partition by deptno order by sal) lastval,
           e.*
      FROM emp e

    结果:

    示例4:

    SELECT first_value(comm ignore nulls) over(partition by deptno order by sal) firstval,
           last_value(comm ignore nulls) over(partition by deptno order by sal) lastval,
           e.*
      FROM emp e

    结果:

    示例5:

    SELECT first_value(sal ignore nulls) over(partition by deptno order by sal) firstval,
           last_value(sal ignore nulls) over(partition by deptno order by sal) lastval,
           e.*
      FROM emp e;
    
    SELECT first_value(sal ignore nulls) over(partition by deptno order by sal) firstval,
           last_value(sal ignore nulls) over(partition by deptno order by sal ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING ) lastval,
           e.*
      FROM emp e

    结果:

    第一个sql结果:

    第二个sql结果:

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  • 原文地址:https://www.cnblogs.com/wolil/p/5550410.html
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