MySQL 中的 LOG2()函数

在本文中，我们将介绍 LOG2()函数，这意味着它将计算以 2 为底的特定数字的对数。

先决条件：LOG函数

MySQL中的LOG2()函数用于计算以2为底的特定数的自然对数，该数必须>0，否则返回NULL。

句法 ：

LOG2( X )

范围 ：
LOG2()函数接受一个参数，如下所述。

• X –我们要计算其以 2 为底的对数值的数字。它应该是正数。

回报：
它返回给定数字 x 以 2 为底的自然对数。

示例-1：
使用 LOG2()函数以 2 为底的给定数字的对数。

SELECT LOG2(16) AS Log2_Val;

输出 ：

Log2_Val
4

Example-2 :
Logarithm of 0 using LOG2() function.

SELECT LOG2(0) AS Log2_Val;

Output :

Log2_Val
NULL

Example-3 :
The LOG2 function can also be used to find the logarithmic value  with base 2 of a column data. To demonstrate create a table named Product.

CREATE TABLE Product
(
    Product_id INT AUTO_INCREMENT,  
    Product_name VARCHAR(100) NOT NULL,
    Buying_price DECIMAL(13,2) NOT NULL,
    Selling_price DECIMAL(13,2) NOT NULL,
    Service_grade Decimal(6,2) NOT NULL,
    PRIMARY KEY(Product_id)

);

Now inserting some data to the Product table :

INSERT INTO Product
(Product_name, Buying_price, Selling_price, Service_grade)
VALUES
    ('Touring Bike' ,2019.00 ,3009.6 ,0.89 ) ,
    ('Mountain Bike' ,3019.50 ,4000.56 ,1.00 ) ,
    ('Road Bike' ,1019.20 ,2000.56 ,-0.89 ) ,
    ('Road Bicycle',1019.50 ,1500.56 ,-1.50 ) ,
    ('Racing Bicycle',3019.50 ,4000.56 ,2.00) ;

Showing all data in Product table :

Select * from Product;

Product_id	Product_name	Buying_price	Selling_price	Service_grade
1	Touring Bike	2019.00	3009.60	0.89
2	Mountain Bike	3019.50	4000.56	1.00
3	Road Bike	1019.20	2000.56	-0.89
4	Road Bicycle	1019.50	1500.56	-1.50
5	Racing Bicycle	3019.50	4000.56	2.00

Now, we are going to find the logarithmic values with base 2 for all the records present in the Service_grade column.

Select 
    Product_id,  
    Product_name,  
    Buying_price,  
    Selling_price,  
    Service_grade,
    LOG2(Service_grade) AS GRADELOG2  
        FROM Product;

Output :

Product_id	Product_name	Buying_price	Selling_price	Service_grade	GRADELOG2
1	Touring Bike	2019.00	3009.60	0.89	-0.16812275880832692
2	Mountain Bike	3019.50	4000.56	1.00	0
3	Road Bike	1019.20	2000.56	-0.89	NULL
4	Road Bicycle	1019.50	1500.56	-1.50	NULL
5	Racing Bicycle	3019.50	4000.56	2.00	1