Question

我需要根据查询结果在mySQL查询中添加一个条件。

SELECT返回了IVC_Recipient我，我想使用此数据作为条件。但这不起作用。

以下是查询：

SELECT 
    KDX_Id, 
    KDX_Name, 
    KDX_FirstName, 
    KDX_Company, 
    BOO_Id, 
    DEB_Date, 
    IFNULL(SUM(IVC_Sum + IVC_Taxes), 0) AS DEB_Total,
    DATEDIFF('2018-07-10', DEB_Date) AS DEB_Nb_Days,
    IVC_Recipient 
FROM ___Debtors 
JOIN ___Invoices 
    ON ___Invoices.IVC_Id = ___Debtors.DEB_InvoiceId 
JOIN ___Bookings 
    ON ___Bookings.BOO_Id = ___Invoices.IVC_BookingId


IF(IVC_Recipient = 'guest') {
    JOIN ___Kardex 
        ON ___Kardex.KDX_Id = ___Bookings.BOO_GuestId
}

IF(IVC_Recipient = 'company') {
    JOIN ___Kardex 
        ON ___Kardex.KDX_Id = ___Bookings.BOO_CompanyId
}

请问我在这里想念什么？

谢谢。

Answer 1

您可以使用CASE表达式：

SELECT 
    KDX_Id, 
    KDX_Name, 
    KDX_FirstName, 
    KDX_Company, 
    BOO_Id, 
    DEB_Date, 
    IFNULL(SUM(IVC_Sum + IVC_Taxes), 0) AS DEB_Total,  -- there is no GROUP BY
    DATEDIFF('2018-07-10', DEB_Date) AS DEB_Nb_Days,
    IVC_Recipient 
FROM ___Debtors 
JOIN ___Invoices 
    ON ___Invoices.IVC_Id = ___Debtors.DEB_InvoiceId 
JOIN ___Bookings 
    ON ___Bookings.BOO_Id = ___Invoices.IVC_BookingId
JOIN ___Kardex 
        ON ___Kardex.KDX_Id = (CASE 
             WHEN IVC_Recipient = 'guest' THEN  ___Bookings.BOO_GuestId
             WHEN IVC_Recipient = 'company' THEN ___Bookings.BOO_CompanyId
             END)

Answer 2

在以下情况下，几乎所有“ if”都可以表示为AND：

JOIN ___Kardex 
    ON (IVC_Recipient = 'guest' AND ___Kardex.KDX_Id = ___Bookings.BOO_GuestId)
    OR (IVC_Recipient = 'company' AND ___Kardex.KDX_Id = ___Bookings.BOO_CompanyId)

...但是根据索引使用的工作方式，有时甚至可以提高性能，使其更简单地加入并在WHERE条件下稍后对结果进行排序（尽管这是我最后的选择，“我们能否获得更多速”）。

JOIN ___Kardex 
    ON  ___Kardex.KDX_Id IN (___Bookings.BOO_GuestId, ___Bookings.BOO_CompanyId)
WHERE (IVC_Recipient = 'guest' AND ___Kardex.KDX_Id = ___Bookings.BOO_GuestId)
    OR (IVC_Recipient = 'company' AND ___Kardex.KDX_Id = ___Bookings.BOO_CompanyId)

使用条件进入MySQL查询

2 个答案: