數據庫---關係代數

原創 子路灬 2020-06-14 16:20

並

相同的部分進行合併，只顯示一次

交

顯示相同的部分

差

顯示不相同的部分

笛卡爾積（X）

顯示所有列，每個元組都要進行組合
在笛卡兒積的結果集中：
- 屬性個數：兩個屬性之和
- 記錄數：兩個記錄數的乘積

投影

選擇屬性的操作

選擇

選擇元組的操作

連接

共有的屬性只保留一個
沒有標明連接條件：默認自然連接（相同屬性等值連接）

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