需要查询逻辑，如何按用户表中的id分组？

Question

我有两张桌子：

INSERT INTO `companies` (`name`) VALUES
('Walmart'),
('Disney'),
('Amazon'),
('Unicom'),
('Microsoft'),
('Intel')

INSERT INTO `users` (`id`, `company`) VALUES
(1, 'Disney'),
(2, 'Amazon'),
(3, 'Intel'),
(3, 'Walmart'),
(4, 'Microsoft'),
(4, 'Unicom'),
(5, 'Microsoft')

结果应如下：

1. 'Walmart', 'Amazon', 'Unicom', 'Microsoft', 'Intel'
2. 'Walmart', 'Disney', 'Unicom', 'Microsoft', 'Intel'
3. 'Disney', 'Amazon', 'Unicom', 'Microsoft'
4. 'Walmart', 'Disney', 'Amazon', 'Intel'
5. 'Walmart', 'Disney', 'Amazon', 'Unicom', 'Intel'

我尝试过：

"SELECT a.name, b.id, b.company FROM users RIGHT JOIN companies ON b.company <> a.name"

这通过省略列表中已有的公司名称来提供正确的逻辑，但问题是它处理相同的ID两次并省略不同的公司名称。如何处理此查询？

Answer 1

以下查询中的基本思想是将包含每个可能的用户/公司组合的日历表连接到users表。 匹配的那些组合将被删除，然后其他公司将使用GROUP_CONCAT汇总为每个用户的CSV字符串。

SELECT t1.id, GROUP_CONCAT(t1.name)
FROM
(
    SELECT DISTINCT u.id, c.name
    FROM users u
    CROSS JOIN companies c
) t1
LEFT JOIN users t2
    ON t1.name = t2.company AND t1.id = t2.id
WHERE t2.company IS NULL
GROUP BY
    t1.id;

Demo

Answer 2

试试这个

int CMainFrame::OnCreate(LPCREATESTRUCT lpCreateStruct)
{
    if (CFrameWndEx::OnCreate(lpCreateStruct) == -1)
        return -1;

    BOOL bNameValid;

    // create a view to occupy the client area of the frame
    if (!m_wndView.Create(NULL, NULL, AFX_WS_DEFAULT_VIEW, CRect(0, 0, 0, 0), this, AFX_IDW_PANE_FIRST, NULL))
    {
        TRACE0("Failed to create view window\n");
        return -1;
    }

    m_wndRibbonBar.Create(this);
    m_wndRibbonBar.LoadFromResource(IDR_RIBBON);

    if (!m_wndStatusBar.Create(this))
    {
        TRACE0("Failed to create status bar\n");
        return -1;      // fail to create
    }

    CString strTitlePane1;
    CString strTitlePane2;
    bNameValid = strTitlePane1.LoadString(IDS_STATUS_PANE1);
    ASSERT(bNameValid);
    bNameValid = strTitlePane2.LoadString(IDS_STATUS_PANE2);
    ASSERT(bNameValid);
    m_wndStatusBar.AddElement(new CMFCRibbonStatusBarPane(ID_STATUSBAR_PANE1, strTitlePane1, TRUE), strTitlePane1);
    m_wndStatusBar.AddExtendedElement(new CMFCRibbonStatusBarPane(ID_STATUSBAR_PANE2, strTitlePane2, TRUE), strTitlePane2);

    // enable Visual Studio 2005 style docking window behavior
    CDockingManager::SetDockingMode(DT_SMART);
    // enable Visual Studio 2005 style docking window auto-hide behavior
    EnableAutoHidePanes(CBRS_ALIGN_ANY);

    return 0;
}


BOOL CMainFrame::OnCreateClient(LPCREATESTRUCT /*lpcs*/,
    CCreateContext* pContext)
{
    return m_wndSplitter.Create(this,
        2, 2,               // TODO: adjust the number of rows, columns
        CSize(10, 10),      // TODO: adjust the minimum pane size
        pContext);
}