Question

我试图学习MySQL存储过程，并且我陷入了一个If ..那么重要。我试图弄清楚如何显示列对IF结果的影响。

这是我的代码，希望您了解我想要做的事情，我的问题出在＆＃34; ...＆＃34;和＆＃34; ...＆＃34; ：

CREATE DEFINER=`root`@`localhost` PROCEDURE `sp_helloworld`()
BEGIN

    SELECT
        ...
        IF pt.is_part_payment = 1 THEN
            pp.due_date AS due_date,
            pp.amount AS amount
        ELSE
            o.due_date AS due_date,
            o.amount AS amount
        END IF;
        ...
    FROM
        orders o
        INNER JOIN payment_types pt ON pt.id = o.payment_type_id 
        INNER JOIN part_payments pp ON pp.order_id = o.order_id
    WHERE
        o.active = 1
END

Answer 1

如您所见，您不能在SQL查询中放置if语句。但是，您可以使用case表达式，但是您必须为每个要单独查询的字段执行此操作：

SELECT
    ...
    CASE pt.is_part_payment WHEN 1 THEN pp.due_date ELSE o.due_date END
        AS due_date,
    CASE pt.is_part_payment WHEN 1 THEN pp.amount ELSE o.amount END AS amount,
...
FROM
    orders o
    INNER JOIN payment_types pt ON pt.id = o.payment_type_id 
    INNER JOIN part_payments pp ON pp.order_id = o.order_id
WHERE
    o.active = 1

如果statement为1则运行特定的SQL语句

1 个答案: