如何显示相关子查询中表的两个详细信息。 #mysql

Question

我想显示套餐的详细信息及其最便宜的子活动的详细信息。假设有 A01,A02,A03 A01 是套餐，A03 是最便宜的儿童活动，所以我的 select 语句应该显示 A01、A03

的详细信息

但是我不明白如何将最便宜的 sub-activity[A03] 的详细信息与 A01 一起显示。

我知道我必须使用相关子查询，但仍然无法正常工作。

现在只显示最便宜的套餐结果。

DDL

CREATE TABLE IF NOT EXISTS `Activity` (
  `ActivityID` VARCHAR(45) NOT NULL,
  `ActivityName` VARCHAR(45) NULL,
  `ActivityCost` float(2) NULL,
  `ActivityType` VARCHAR(45) NULL);

CREATE TABLE IF NOT EXISTS `Package` (
  `PackageActivityID` VARCHAR(45) NOT NULL,
  `ChildActivityID` VARCHAR(45) NOT NULL,
  INDEX `fk_Package_Activity1_idx` (`PackageActivityID` ASC) VISIBLE,
  INDEX `fk_Package_Activity2_idx` (`ChildActivityID` ASC) VISIBLE,
  CONSTRAINT `fk_Package_Activity1`
    FOREIGN KEY (`PackageActivityID`)
    REFERENCES `mydb`.`Activity` (`ActivityID`)
  CONSTRAINT `fk_Package_Activity2`
    FOREIGN KEY (`ChildActivityID`)
    REFERENCES `mydb`.`Activity` (`ActivityID`);

insert into activity values ('A01', 'Kayaking', 120, 'B');
insert into activity values ('B01', 'Seaking', 420, 'I');
insert into activity values ('C01', 'maya', 220, 'O');
insert into activity values ('D01', 'bing', 170, 'B');

insert into package (packageactivityid, childactivityid) values ('A01','C01');
insert into package (packageactivityid, childactivityid) values ('F01','F01');
insert into package (packageactivityid, childactivityid) values ('D01','D01');
insert into package (packageactivityid, childactivityid) values ('E01','E01');
insert into package (packageactivityid, childactivityid) values ('B01','B01');

回顾一下，我希望能达到这个结果：

+-------------------+-----------------+------------+--------------+--------------+--------------+
| PackageActivityID | ChildActivityID | ActivityID | ActivityName | ActivityCost | ActivityType |
+-------------------+-----------------+------------+--------------+--------------+--------------+
| A01               | C01             | A01        | Kayaking     |          120 | B            |
| A01               | C01             | A01        | Kayaking     |          120 | B            |
| A01               | C01             | A01        | Kayaking     |          120 | B            |
| A01               | C01             | A01        | Kayaking     |          120 | B            |
| D01               | D01             | D01        | bing         |          170 | B            |
| D01               | D01             | D01        | bing         |          170 | B            |
| D01               | D01             | D01        | bing         |          170 | B            |
| D01               | D01             | D01        | bing         |          170 | B            |
| B01               | B01             | B01        | Seaking      |          420 | I            |
| B01               | B01             | B01        | Seaking      |          420 | I            |
| B01               | B01             | B01        | Seaking      |          420 | I            |
| B01               | B01             | B01        | Seaking      |          420 | I            |
+-------------------+-----------------+------------+--------------+--------------+--------------+

我尝试的查询：

select activityid, activityname, activitycost 
from package p, activity a
where p.PackageActivityID = a.ActivityID
and p.ChildActivityID = (select ActivityID
from package p,activity a
where a.activityid = p.ChildActivityID
having min(activitycost));

我的查询只显示 packageactivity 的详细信息，不显示 childactivity 的详细信息。

Answer 1

如果我没看错，你可以使用window函数：

select p.*, a.*
from package p
inner join (
    select a.*, rank() over(partition by activityid order by activitycost) rn
    from activity a
) a on p.PackageActivityID = a.activityid
where a.rn = 1

基本上，这会为每个包裹带来更便宜 activity 的较少细节 - 这就是我对你的问题的理解。此处允许打领带。

在 MySQL < 8.0 中，window 函数不可用，替代方法是使用相关子查询进行过滤：

select p.*, a.*
from package p
inner join activity a  on p.PackageActivityID = a.activityid
where a.activitycost = (
    select min(a1.activitycost)
    from activity a1
    where a1.activityid = a.activityid
)

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