mysql - 嵌套查询和联合分组 (SQL)

Question

我需要帮助编写查询以获取一些信息，但我无法编写它。

[table_People]
int id
var name

[table_Tools]
int id
var name

[table_Activity1]
int person_id
int tool_id
date delivery_date

[table_Activity2]
int person_id
int tool_id
date installation_date

该查询需要返回所有人员的列表以及他们在活动 1 或 2 中使用的最新工具的名称（两者之间发生的最新活动）。

SELECT
    people.id   AS personId,
    people.name AS personName,
    (
        SELECT
            tools.name AS toolName
        FROM
            activity1
        JOIN
            tools ON tools.id=activity1.tool_id
        WHERE
            activity1.id=people.id
        UNION ALL
        SELECT
            tools.name AS toolName
        FROM
            activity2
        JOIN
            tools ON tools.id=activity2.tool_id
        WHERE
            activity2.id=people.id
        ORDER BY
            installationDate,deliveryDate
    ) AS toolName
FROM
    people
ORDER BY
    people.name
ASC

我遇到的问题是我无法按日期（交付或安装）排序，因为我收到错误，因为它们是不同的列名。

score 4 · Accepted Answer

在子查询中使用 UNION 会创建一个派生的临时表。未选择的列不在结果集中，因此您不能对不在 SELECT 子句中的列进行 ORDER。

使用 UNION 时，SELECT 子句中使用的第一个列名将用于结果集中（类似于别名，尽管您也可以使用别名）。

只需确保在 SELECT 子句中命名列。

您还需要一个 LIMIT 子句将子查询限制为单行：

SELECT
    people.id   AS personId,
    people.name AS personName,
    (
        SELECT
            tools.name AS toolName, delivery_date
        FROM
            activity1
        JOIN
            tools ON tools.id=activity1.tool_id
        WHERE
            activity1.id=people.id
        UNION ALL
        SELECT
            tools.name AS toolName, installation_date
        FROM
            activity2
        JOIN
            tools ON tools.id=activity2.tool_id
        WHERE
            activity2.id=people.id
        ORDER BY
            deliveryDate
        LIMIT 1
    ) AS toolName
FROM
    people
ORDER BY
    people.name
ASC

这是一个更简单的例子来说明这个问题：

SELECT fish FROM sea
UNION
SELECT dog FROM land
ORDER BY fish

是相同的：

SELECT fish AS animal FROM sea
UNION
SELECT dog AS animal FROM land
ORDER BY animal

结果被放入一个派生的临时表中，您可以随意命名列，但您使用的第一个名称会保留。

score 2 · Accepted Answer

我的解决方案将联合放在一个子查询中，然后按它们排序。您只需要第一行，因此您需要一个限制子句（或在 Oracle 中为 rownum = 1 或在 MSSQL 中为 top 1）：

SELECT people.id   AS personId,
       people.name AS personName, 
       (SELECT toolname
        FROM ((SELECT tools.name AS toolName, delivery_date as thedate
               FROM activity1 a
               WHERE a.PersonId = people.id
              ) union all
              (SELECT tools.name AS toolName, installation_date as thedate
               FROM activity2 a
               WHERE a.PersonId = people.id
              )
             ) a join
             tools t
             on a.toolsid = t.toolsid
        order by 2 desc
        limit 1
       ) AS toolName
FROM people
ORDER BY people.name ASC

为了简化查询，我还删除了工具的最内层连接。

score 0 · Accepted Answer

SELECT
    p.id             AS person_id
  , p.name           AS person_name
  , CASE WHEN COALESCE(a1.delivery_date, '1000-01-01')
              > COALESCE(a2.installation_date, '1000-01-01')
           THEN t1.name
           ELSE t2.name
    END              AS tool_name
FROM 
    People AS p
  LEFT JOIN 
    Activity1 AS a1
        ON (a1.tool_id, a1.delivery_date) =
           ( SELECT tool_id, delivery_date
             FROM Activity1 AS a
             WHERE a.person_id = p.id
             ORDER BY delivery_date DESC
             LIMIT 1
           )
  LEFT JOIN 
    Tools AS t1
        ON t1.id = a1.tool_id
  LEFT JOIN 
    Activity2 AS a2
        ON (a2.tool_id, a2.installation_date) =
           ( SELECT tool_id, installation_date
             FROM Activity2 AS a
             WHERE a.person_id = p.id
             ORDER BY installation_date DESC
             LIMIT 1
           )
  LEFT JOIN 
    Tools AS t2
        ON t2.id = a2.tool_id

score 0 · Accepted Answer

做

SELECT
    people.id   AS personId,
    people.name AS personName,
    IF (
        (SELECT
            deliveryDate AS dDate
        FROM
            activity1
        WHERE
            person_id=personId) --assuming you have only one row returned here, else limit by some condition
        >
        (SELECT
            installationDate AS iDate
         FROM
            activity2
         WHERE
            person_id=personId) --assuming you have only one row returned here, else limit by some condition
         , (SELECT
                tools.name AS toolName
            FROM
                activity1
            JOIN
                tools ON tools.id=activity1.tool_id
            WHERE
                activity1.person_id=personId)
         , (SELECT
                tools.name AS toolName
            FROM
                activity2
            JOIN
                tools ON tools.id=activity2.tool_id
            WHERE
                activity2.person_id=personId)
           ) AS toolName
FROM
    people        
ORDER BY
    people.name
ASC

此查询假定活动表中只有每个人的记录。如果还有更多，您需要根据总和最大条件限制您的选择结果集，或者只有您知道。

score 0 · Accepted Answer

如果在select.

例如：

select name from people order by name

select a1.delivery_date, t.name from activity1 a1, tools t 
order by a1.delivery_date,t.name

投影的所有选定列也必须在定义中order by定义。在您的示例中，两个 select 语句都在使用，tools.name as toolname但您想按其他列排序。

score 0 · Accepted Answer

MySQL 版本（可能您可以从中获得更紧凑的代码）：

Select * from 
(
  Select toolName, person_id, Max(TargetDate) as MaxDate
  From
        (
            SELECT tools.name AS toolName, activity1.person_id, activity1.delivery_date as targetDate
            FROM
                activity1
            JOIN
                tools ON tools.id=activity1.tool_id
            UNION ALL
            SELECT
                tools.name AS toolName, activity2.person_id, activity2.installation_date as TargetDate
            FROM
                activity2
            JOIN
                tools ON tools.id=activity2.tool_id
        )
 Group by toolName, person_id

) preselect
    join
    (
    Select toolName, person_id, Max(TargetDate)
    From
            (
                SELECT tools.name AS toolName, activity1.person_id, activity1.delivery_date as targetDate
                FROM
                    activity1
                JOIN
                    tools ON tools.id=activity1.tool_id
                UNION ALL
                SELECT
                    tools.name AS toolName, activity2.person_id, activity2.installation_date as TargetDate
                FROM
                    activity2
                JOIN
                    tools ON tools.id=activity2.tool_id
            )) result on result.toolName = preselect.toolName and result.person_id = preselect.person_id and result.TargetDate = preselect.MaxDate

score 0 · Accepted Answer

选择 people.id 作为 person_id，people.name 作为 person_name，tools.name 作为来自 table_people 的工具名人们离开加入（选择安装日期>交付日期然后 act2.tool_id 的情况，否则 act1.tool_id 结束为最近的_工具_id，安装日期>交付日期的情况，然后是 act2。 person_id else act1.person_id end as recent_most_person_id from table_activity1 act1 内部连接 table_activity2 act2 on act1.person_id=act2.person_id)X on people.id=X.recent_most_person_id 内部连接 table_tools tools.id=X.recent_most_tool_id

mysql - 嵌套查询和联合分组 (SQL)

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