用pgSQL改写这段代码，使用游标获取指定 empno 的员工的每条工资记录中的工资数额。使 用 LOOP 语句编写循环。DELIMITER // CREATE PROCEDURE calc_avg_and_var_salary_for_emp_no(IN emp_no_in INT, OUT AVG REAL, OUT var REAL) BEGIN DECLARE done INT DEFAULT 1; DECLARE sal REAL; DECLARE num INT; DECLARE cur1 CURSOR FOR SELECT salary FROM salaries WHERE emp_no = emp_no_in; DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 0; SET var = 0, AVG = 0, num = 0; OPEN cur1; FETCH cur1 INTO sal; WHILE done = 1 DO SET AVG = AVG + sal; SET var = var + sal*sal; SET num = num + 1; FETCH cur1 INTO sal; END WHILE; CLOSE cur1; SET AVG = AVG/num; SET var = var/num - AVG*AVG; END// DELIMITER ;

CREATE OR REPLACE FUNCTION calc_avg_and_var_salary_for_emp_no(IN emp_no_in INT, OUT AVG REAL, OUT var REAL)
AS $$
DECLARE 
    done INT DEFAULT 1;     
    sal REAL;     
    num INT; 	
    cur1 CURSOR FOR SELECT salary FROM salaries WHERE emp_no = emp_no_in;	 	
BEGIN
    SET var = 0;
    SET AVG = 0;
    SET num = 0;
    OPEN cur1;
    FETCH cur1 INTO sal;
    WHILE done = 1 LOOP 
        SET AVG = AVG + sal;
        SET var = var + sal*sal;
        SET num = num + 1;
        FETCH cur1 INTO sal;
        IF NOT FOUND THEN
            SET done = 0;
        END IF;
    END LOOP;
    CLOSE cur1;
    SET AVG = AVG/num;
    SET var = var/num - AVG*AVG;
END
$$ LANGUAGE plpgsql;

使用游标获取指定 empno 的员工的每条工资记录中的工资数额，使用了 `CURSOR`；

使用 `LOOP` 语句编写循环；

增加了 `IF NOT FOUND THEN` 来判断是否到达游标末尾。