3-关系运算理论

3-关系运算理论

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3 关关关关关关关关
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关关关关 关关关关关关关关关关关关关关——关关关关关关关关关关关关关关关关关关关关关关关关关关关关 关关关关关关关关关关关关关关关关关关关关关关关
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关关关关关关关关关关关关关关关关关关关关关关关关关关关关关关关关关关关关关关关关 关关关关关关关关关关关关关关关关关关关关关关关关关关关关关
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3.1 关关关关关关 关关关关关关关 关关关关关关关 关关关关关 关关关关关关关关关 关关关关关 关关关关关关关关关关关 关关关关 关关关关
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3.1.1 关 Union ( ) R 关 S 关关关 R S 关关关 R 关 S 关关关关关关关关关关 关关关关关关关关关关关关关 R 关 S 关关关关关关关关关关关关关关关关关关关关关关关关关关
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3.1.2 关 Intersect (∩) R 关 S 关关关 R∩S 关关关 R 关 S 关关关关关关关关关关 关关关关关关关关关关关关关 R 关 S 关关关关关关关关关关关关关关关关关关关关关关关关关关
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3.1.3 关 Minus (-) R 关 S 关关关 R-S 关关关 R 关关关关 S 关关关关关关关 R 关 S 关关关关关关关关关关关关关关关关关关关关关关关关关关
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3.1.4 关关 Projection(π) 关关关 R 关关关关关关关关关关关关关 π A 1, A 2,…, A n (R), 关关关 R 关关关关关关 A 1 ,A 2 ,…,A n 关关关关关关 关关关关 关关关关关关关关 , 关关关关关关关关关关关 关 : π ssex,sage (student) ?
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3.1.5 关关关关 (×) 关关 R 关 S 关关关关关关关关关关关关关关关关关关关关关关关关 R×S 关 关关关 R 关 S 关关关关关关关关
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3-关系运算理论

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