Question

我有以下查询，它从一系列表中获取一堆列

SELECT Events.eventID, Events.eventName, Organisations.organisationName, Events.eventCrewSize, Events.eventGuestSize, Events.eventDate, Events.eventTime, Boat.boatName, Address.addressNo, Address.addressStreet, Address.addressStreetType, Address.addressSuburb, Address.addressPostCode, Address.addressState 
FROM Events, Organisations, Boat, Address 
WHERE Events.eventOrganisation = Organisations.organisationID AND Events.eventBoatID = Boat.boatID AND Events.eventAddressID = Address.addressID AND Events.eventDate >= CURDATE();

我的问题是，并非所有事件都具有组织，并且没有为该列返回NULL，而是没有组织就不包括任何事件。

我尝试从where子句中删除组织部分，其中包括空行，但它使用另一个事件的组织作为其值，而不是其实际的空值。

我认为这是一个联接问题，但不确定如何相应地构造它。

Answer 1

您可以尝试使用左联接

SELECT Events.eventID, Events.eventName, Organisations.organisationName, Events.eventCrewSize, Events.eventGuestSize, Events.eventDate, Events.eventTime, Boat.boatName, Address.addressNo, Address.addressStreet, Address.addressStreetType, Address.addressSuburb, Address.addressPostCode, Address.addressState 
FROM Events 
LEFT JOIN Organisations on Events.eventOrganisation = Organisations.organisationID
LEFT JOIN Boat on Events.eventBoatID = Boat.boatID
LEFT JOIN Address on Events.eventAddressID = Address.addressID
WHERE Events.eventDate >= CURDATE();

不要忘记在主键和外键/规范化之间应用关系。您可以使用NULLIF()来避免空值

不能正确加入

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