mysql函数怎么写

CREATE FUNCTION function_name (parameter_list)
RETURNS data_type
[characteristic ...]
BEGIN
    -- SQL statements
END;

DELIMITER //

CREATE FUNCTION AddNumbers(a INT, b INT)
RETURNS INT
DETERMINISTIC
BEGIN
    RETURN a + b;
END;

//

DELIMITER ;

SELECT AddNumbers(3, 5); -- 返回 8

CREATE FUNCTION function_name (parameter_list)
RETURNS TABLE
[column_definition ...]
[characteristic ...]
RETURN [expression];

DELIMITER //

CREATE FUNCTION GetEmployeesByDepartment(department_id INT)
RETURNS TABLE
(
    employee_id INT,
    employee_name VARCHAR(255),
    department_name VARCHAR(255)
)
DETERMINISTIC
RETURN
(
    SELECT e.employee_id, e.employee_name, d.department_name
    FROM employees e
    JOIN departments d ON e.department_id = d.department_id
    WHERE e.department_id = department_id
);

//

DELIMITER ;

SELECT * FROM GetEmployeesByDepartment(1);

CREATE FUNCTION function_name (parameter_list)
RETURNS @return_table TABLE (column_definition ...)
[characteristic ...]
BEGIN
    -- SQL statements
END;

DELIMITER //

CREATE FUNCTION GetEmployeeSalaries()
RETURNS @employee_salaries TABLE
(
    employee_id INT,
    salary DECIMAL(10, 2)
)
DETERMINISTIC
BEGIN
    INSERT INTO @employee_salaries (employee_id, salary)
    SELECT employee_id, salary FROM salaries;
    
    RETURN;
END;

//

DELIMITER ;

SELECT * FROM GetEmployeeSalaries();