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我有關於如何執行SQL查詢的問題。我寫了一個我在這裏使用的示例數據庫,我試圖讓所有想要幫助的人保持簡單。SQL根據不同的表關係找到最經常性的元素
Officer Permit Vehicle Dispatch
Oid | Dname | Rank Oid | Type | Model Vid | Type | Model Did | Oid | Location
------------------ ------------------ ------------------ --------------
1 | John | Jr 1 D1 Ford 1 D1 Ford 1 1 Hill
2 | Jack | Sr 1 D2 Ford 2 D2 Ford 2 2 Beach
3 | Jay | Jr 2 D1 Ford 3 D3 Ford 3 3 Post
4 | Jim | Jr 3 D1 Ford 4 D4 Ford 4 1 Beach
5 | Jules | Sr 5 D1 Ford 5 D5 Ford 5 2 Hill
1 D3 Ford 6 4 Post
2 D2 Ford 7 5 Hill
4 D1 Ford 8 5 Beach
1 D5 Ford 9 2 Post
表之間的關係是:
Officer - lists the officer by OID(officer ID)/Name/Rank where Sr is highest, Jr is lowest.
Permit - Officers are required to have a permit depending on the vehicle they will be using, Oid for Officer ID, Type for the vehicle and Model.
Vehicle - Vid for vehicle ID, Type and Model
Dispatch - Did for Dispatch ID, keeps track of which officer (Oid) was dispatched to which location (Location)
問:我需要知道兩件事情從這裏開始。 首先是我怎麼知道哪個軍官被允許駕駛所有車型? 二是如何知道哪個官員已派往所有派遣的地點?
編寫這兩個查詢對我來說是一場噩夢,我嘗試過加入不同的表格,但是我仍然無法從其中獲得最經常性的元素(我不知道該怎麼做!),任何幫助都將不勝感激!
我確實看到它,非常好我將盡快測試它。順便說一句,您使用關鍵字'有',這使事情變得更簡單。但是,有沒有辦法做到這一點,而不使用它? – AGE
'SELECT ... HAVING'主要相當於SELECT * from(SELECT ...)WHERE '。 –
Barmar