Technology Sharing

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Conditional Function

• IF(): If a condition is true, return one value, otherwise return another value.

-- 示例：根据员工的薪水返回薪水等级  
SELECT name, salary,  
       IF(salary < 3000, 'Low',  
          IF(salary BETWEEN 3000 AND 7000, 'Medium', 'High')) AS salary_level  
FROM employees;

• CASE: More complex conditional logic, similar to switch-case statements in programming languages.

SELECT 
    CASE 
        WHEN score >= 90 THEN 'A'
        WHEN score >= 80 THEN 'B'
        WHEN score >= 70 THEN 'C'
        WHEN score >= 60 THEN 'D'
        ELSE 'F'
    END AS grade
FROM students;

• COALESCE(): Returns the first non-NULL value in the parameter list.

SELECT name, COALESCE(city, 'Unknown') AS city
FROM students;

Encryption Function

• MD5(): Calculates the MD5 hash value of a string.

-- 示例：对用户的密码进行MD5加密  
SELECT MD5('password123') AS encrypted_password;

• SHA1(): Calculates the SHA-1 hash value of a string.

SELECT SHA1('7895656')

Conversion functions

• CAST(): Converts an expression to a specified data type.

-- 示例：将字符串转换为整数  
SELECT CAST('123' AS UNSIGNED) AS number;

• CONVERT(): The function is similar to CAST() and is used for type conversion.

-- 示例：将日期字符串转换为日期类型  
SELECT CONVERT('2023-01-01', DATE) AS converted_date;