zoukankan      html  css  js  c++  java
  • LNNVL函数使用

          显示那些佣金比例(commision)不大于20%或者为NULL的员工的信息。

    CREATE TABLE plch_employees
    (
        employee_id      INTEGER PRIMARY KEY
    ,  last_name        VARCHAR2 (100)
    ,  salary           NUMBER
    ,  commission_pct   NUMBER
    );
    INSERT INTO plch_employees   VALUES (100,  'Picasso',  1000000 ,  .3);
    INSERT INTO plch_employees VALUES (200,  'Mondrian',  1000000,  .15);
    INSERT INTO plch_employeesVALUES (300,  'O''Keefe',  1000000,  NULL);
    COMMIT;

    SQL> SELECT last_name,e.salary,e.commission_pct
           FROM plch_employees e
          WHERE e.commission_pct <= .2
             OR e.commission_pct IS NULL;
    LAST_NAME           SALARY COMMISSION_PCT
    --------------- ---------- --------------
    Mondrian           1000000            .15
    O'Keefe            1000000


    SQL> SELECT last_name,e.salary,e.commission_pct
           FROM plch_employees e
         WHERE LNNVL (e.commission_pct > .2);
    LAST_NAME           SALARY COMMISSION_PCT
    --------------- ---------- --------------
    Mondrian           1000000            .15
    O'Keefe            1000000


    LNNVL 解释:

    LNNVL provides a concise way to evaluate a condition when one or both operands of the condition may be null. The function can be used only in the WHERE clause of a query. It takes as an argument a condition and returns TRUE if the condition is FALSE or UNKNOWN and FALSE if the condition is TRUELNNVL can be used anywhere a scalar expression can appear, even in contexts where the IS [NOTNULLAND, or OR conditions are not valid but would otherwise be required to account for potential nulls. Oracle Database sometimes uses the LNNVL function internally in this way to rewrite NOT IN conditions as NOT EXISTS conditions. In such cases, output from EXPLAIN PLAN shows this operation in the plan table output. The condition can evaluate any scalar values but cannot be a compound condition containing ANDOR, or BETWEEN.

    The table that follows shows what LNNVL returns given that a = 2 and b is null.

    ConditionTruth of ConditionLNNVL Return Value
    a = 1 FALSE TRUE
    a = 2 TRUE FALSE
    IS NULL FALSE TRUE
    b = 1 UNKNOWN TRUE
    IS NULL TRUE FALSE
    a = b UNKNOWN TRUE


          大致的意思是:lnnvl用于某个语句的where子句中的条件,如果条件为true就返回false;如果条件为UNKNOWN或者false就返回true。该函数不能用于复合条件如AND, OR, or BETWEEN中。

  • 相关阅读:
    《学习之道》第六章习惯的部分-信号
    《学习之道》第六章习惯的组成
    《学习之道》第六章习惯的形成
    《学习之道》第五章小恶魔造成拖延(二)
    《学习之道》第五章拖延的两个小案例
    《学习之道》第五章是借口造成拖延(一)
    《学习之道》第五章认识拖延
    《学习之道》第五章认识“小恶魔”
    《学习之道》第五章分心与拖延
    redis 安装
  • 原文地址:https://www.cnblogs.com/riasky/p/3363587.html
Copyright © 2011-2022 走看看