mysql里面怎么取绝对值

ABS(expression)

CREATE TABLE employees (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(100),
    salary DECIMAL(10, 2)
);

INSERT INTO employees (name, salary) VALUES ('Alice', -5000.00);
INSERT INTO employees (name, salary) VALUES ('Bob', 3000.00);
INSERT INTO employees (name, salary) VALUES ('Charlie', -2000.00);

SELECT name, ABS(salary) AS absolute_salary FROM employees;

+---------+-----------------+
| name    | absolute_salary |
+---------+-----------------+
| Alice   | 5000.00         |
| Bob     | 3000.00         |
| Charlie | 2000.00         |
+---------+-----------------+