Oracle数值型函数LN(y)的使用小结

LN(y)

SELECT 
    EXP(3) AS e的三次方,          -- 返回20.0855369
    LN(20.0855369) AS 还原指数,   -- 返回3
    EXP(-3) AS e的负三次方,       -- 返回0.049787068
    LN(0.049787068) AS 负指数还原 -- 返回-3
FROM dual;

SELECT 
    LN(EXP(1)) AS 验证e,  -- 返回1
    EXP(LN(2.7182818)) AS 反向验证 -- 返回2.7182818
FROM dual;

-- 计算投资翻倍所需时间（72法则精确版）
SELECT 
    interest_rate,
    LN(2)/LN(1 + interest_rate) AS 精确翻倍年限
FROM investment_products;

-- 对数转换处理右偏分布
SELECT 
    user_value,
    LN(user_value + 1) AS 正态化处理值
FROM skewed_data;

-- 计算对数似然函数值
SELECT 
    SUM(LN(probability)) AS 对数似然值
FROM probability_distribution;

-- 计算需求价格弹性
SELECT 
    REGR_SLOPE(LN(quantity), LN(price))) AS 价格弹性系数
FROM sales_data;

SELECT 
    EXP(LN(15)) AS 验证1,  -- 返回15
    LN(EXP(2.5)) AS 验证2  -- 返回2.5
FROM dual;

-- 换底公式：LN(y) = LOG(x,y) * LN(x)
SELECT 
    LN(100) AS 自然对数,
    LOG(10,100) * LN(10) AS 换底结果
FROM dual;

SELECT 
    LN(10) AS 自然对数,
    LOG(10,10) AS 常用对数,
    LOG(2,10) AS 二进制对数
FROM dual;

SELECT 
    LN(0) AS 零值测试,      -- 报错：ORA-01428
    LN(-5) AS 负值测试,     -- 报错：ORA-01428
    LN(NULL) AS 空值测试    -- 返回NULL
FROM dual;

-- 创建函数索引加速查询
CREATE INDEX idx_ln_salary ON employees(LN(salary + 1));

-- 物化视图预计算结果
CREATE MATERIALIZED VIEW mv_ln_values
REFRESH COMPLETE
AS SELECT id, LN(value) AS ln_value FROM source_data;

-- 使用BINARY_DOUBLE提高精度
SELECT 
    LN(BINARY_DOUBLE '1234.5678') AS 高精度结果
FROM dual;