mysql 结果输出到变量

DELIMITER //

CREATE PROCEDURE GetTotalSales()
BEGIN
    DECLARE total_sales DECIMAL(10, 2);

    -- 查询总销售额并存储到变量中
    SELECT SUM(sale_amount) INTO total_sales FROM sales;

    -- 输出结果
    SELECT total_sales;
END //

DELIMITER ;

DELIMITER //

CREATE PROCEDURE GetTotalSales()
BEGIN
    DECLARE total_sales DECIMAL(10, 2);

    -- 查询总销售额并存储到变量中，使用 IFNULL 处理空值
    SELECT IFNULL(SUM(sale_amount), 0) INTO total_sales FROM sales;

    -- 输出结果
    SELECT total_sales;
END //

DELIMITER ;

DELIMITER //

CREATE PROCEDURE GetTotalSales()
BEGIN
    DECLARE total_sales DECIMAL(10, 2);
    DECLARE done INT DEFAULT FALSE;

    DECLARE cur CURSOR FOR SELECT sale_amount FROM sales;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

    OPEN cur;

    read_loop: LOOP
        FETCH cur INTO total_sales;
        IF done THEN
            LEAVE read_loop;
        END IF;
    END LOOP;

    CLOSE cur;

    -- 输出结果
    SELECT total_sales;
END //

DELIMITER ;