Question

我试图展示商家以及最高折扣优惠。但我仍然希望展示没有报价的企业。

商家存储在<tr v-for="item in items"> <td> <span id="TRIGGER" @click="visible = item.name">{{item.name}}</span> <div id="SHOW-HIDE-DIV" v-show="visible === item.name"></div> </td> </tr>

中

business_tb

这些商家提供的折扣存储在business_id | business_name ------------+--------------- 1 | aaa 2 | bbb 3 | ccc

中

deal_offer_tb

和折扣类型存储在deal_offer_id | business_id | deal_id --------------+-------------+---------- 1 | 1 | 3 2 | 1 | 2 3 | 2 | 0 4 | 1 | 1 5 | 3 | 3。

deal_tb

所以我想要的显示应该是这样的：

deal_id | discount
--------+----------
    1   |    40%
    2   |    30%
    3   |    20%
    4   |    10%

但是我目前的查询：

 1 |  aaa | 40%
 2 |  bbb | ---
 3 |  ccc | 20%

我只得到：

SELECT a.business_id, a.business_name, c.discount
    FROM business_tb a
    LEFT JOIN (SELECT min(deal_id) AS deal_id, business_id FROM deal_offer_tb GROUP BY business_id) b ON a.business_id = b.business_id
    LEFT JOIN deal_tb c ON b.deal_id = c.deal_id

它不显示没有提供折扣的商家。

我怎么想得到我想要的输出？

更新：我不知道之前发生了什么，但我的查询按照我想要的方式运行。感谢那些回答的人的努力。欣赏它，大时间！

Answer 1

我会通过使用子查询来查找每个业务的最大折扣，加入deal_offer_tb和deal_tb表。然后，将此子查询连接到business_tb表以获取最终结果。请注意，我使用初始LEFT JOIN来说明某个商家甚至可能没有与之相关的交易。在这种情况下，我为该业务分配了最大折扣0（这是有道理的，因为那时将适用完整的正常价格）。

SELECT
    t1.business_id,
    t1.business_name,
    COALESECE(t2.max_discount, 0) AS max_discount
FROM business_tb t1
LEFT JOIN
(
    SELECT t1.business_id, MAX(t2.discount) AS max_discount
    FROM deal_offer_tb t1
    INNER JOIN deal_tb t2
        ON t1.deal_id = t2.deal_id
    GROUP BY t1.business_id
) t2
    ON t1.business_id = t2.business_id

Answer 2

此查询基本上是您的查询（带表别名）：

SELECT b.business_id, b.business_name, d.discount
FROM business_tb b LEFT JOIN
     (SELECT MIN(deal_id) AS deal_id, business_id
      FROM deal_offer_tb dot
      GROUP BY business_id
     ) dot
     ON b.business_id = dot.business_id LEFT JOIN
     deal_tb d
     ON d.deal_id = dot.deal_id;

根据LEFT JOIN的定义，无论business_tb子句的其余部分是否存在匹配，它都会将所有行保留在FROM中。您没有其他过滤（通过WHERE）或聚合。因此，这应返回business_tb中的所有行。

Answer 3

以下是进行查询的一种方法：

SELECT
    a.business_id, a.business_name, b.max
FROM business_tb a
INNER JOIN (
    SELECT
        c.business_id, MAX(d.discount) AS max
    FROM deal_offer_tb c
    LEFT JOIN deal_tb d ON c.deal_id = d.deal_id
    GROUP BY c.business_id
) b ON a.business_id = b.business_id;

deal_id中没有deal_tb 0，所以我认为null deal_offer_id为COMPUTE count=XDATE.WEEK(date).。

显示最高报价，但仍然显示没有报价

3 个答案: