Question

我有3个表1）用户（userId，年龄）2）购买（purchaseId，userId，itemId，date）3）项目（itemId，price）。目标是编写一个查询，以显示按月分组的每个用户的平均购买金额。我目前还不确定我是否需要第一张桌子，到目前为止，我已经这样了：

SELECT Purchases.userid, Purchases.date, Purchases.itemId Items.itemId, AVG(SUM(Items.price))
FROM Purchases
INNER JOIN Purchases.itemId ON Items.itemId
GROUP BY (somehow group by month)

我被困住了。你能解释一下，如何编写这样的查询。很抱歉，我没有表的示例或正确的输出示例，因为它是一个测试任务。谢谢！

Answer 1

在SQL Server中：

    {
"fields": {
    "project": {
        "key": "MFS"
    },
    "summary": "Test Jira Integration API --Testing New XtremeJira Interface",
    "description": "DonTest Jira Integration API ",
    "issuetype": {
        "name": "Defect"
    },
    "fixVersions": [{
        "name": "MFS 15.1.0"
    }, {
        "name": "MFS 15.6.2"
    }],
    "customfield_10182": "1002",
    "priority": {
        "name": "Major",
        "id": "3"
    },
    "versions": [{
        "name": "MFS 15.1.0"
    }, {
        "name": "MFS 15.6.2"
    }],
    "assignee": {
        "name": "kartik"
    },
    "components": [],
    "environment": ""
}}

Answer 2

你可以试试这个。

SELECT Purchases.userid, MONTH(Purchases.date), AVG(Items.price)
FROM Purchases
INNER JOIN Items ON  Purchases.itemId = Items.itemId
GROUP BY Purchases.userid, MONTH(Purchases.date)

Answer 3

按月分组需要在＆＃34;桶中添加日期＆＃34;与该日期相关的年份和月份。每种数据库类型都有它自己独特的功能集，例如

--MS SQL Server
SELECT Purchases.userid, Purchases.itemId, year(Purchases.date), month(Purchases.date), AVG(Items.price)
FROM Purchases
GROUP BY Purchases.userid, Purchases.itemId, year(Purchases.date), month(Purchases.date)

--Oracle
SELECT Purchases.userid, Purchases.itemId, trunc(Purchases.date,'YYYYMM'), AVG(Items.price)
FROM Purchases
GROUP BY Purchases.userid, Purchases.itemId, trunc(Purchases.date,'YYYYMM')

Answer 4

您不能使用AVG(SUM(Items.price))

之类的双重汇总

因此，您可能成为获得SUM然后使用AVG

的子查询

在SQL Server中：

SELECT 
    Purchases.userid, 
    YEAR(Purchases.date), 
    MONTH(Purchases.date), 
    Purchases.itemId 
    Items.itemId, 
    AVG(Items.SumPrice)
FROM
    Purchases 
INNER JOIN
    Users T2 ON Purchases.userId = T2.userId
INNER JOIN 
    (SELECT 
         itemId, SUM(price) AS SumPrice
     FROM  
         Items
     GROUP BY 
         itemId) AS Items ON Items.itemId
GROUP BY  
    Purchases.userid, Purchases.itemId, 
    YEAR(Purchases.date), 
    MONTH(Purchases.date),
    Items.itemId

按月分组的每个用户的平均总和

4 个答案: