關係代數 數據庫中的連接

原創 InAHurryv 2020-06-06 15:35
  • θ連接：邏輯上是先做笛卡爾積 在做選擇操作 而等值連接 是其特列
  • 等值連接 :inner join可以對同一張表進行 等值連接 不會刪除重複的列
  • 外連接：左外連接 右外連接 全外連接
  • 自然連接： 自動以相等的列作爲連接點 會刪除重複的列
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