题目
题目

INFO20003_2025_SM2 MINI Practice Exam

匹配题

RA For each of the relational algebra below, state whether they are correct or not for the following statement:   List the topics of forums where the general user with user id “1” has posted at least once before the date “01-01-2022”.           1: A 2: B 3: C 4: D

选项
A.No
B.Yes
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思路分析
We start by restating the task and the options to ensure clarity. Question: For each of the relational algebra below, state whether they are correct or not for the following statement: List the topics of forums where the general user with user id “1” has posted at least once before the date “01-01-2022”. Options for each subpart (a–d): a) πForum.Topic (σ Post.WhenPosted<01-01-2022 ∧ Post.PostedBy=1 (Post ⋈ Post.Forum = Forum.Id Forum)) b) σForum.Topic (τ Post.WhenPosted<01-01-2022 ∧ Post.PostedBy=1 (Post ⋈ Post.Forum = Forum.Id Forum)) c) πForum.Topic (σ Post.WhenPosted<01-01-2022 ∧ Post.PostedBy=1 (Post ⋈ Post.Forum = Forum.Id Forum)) d) πForum.Topic (σPost.WhenPosted<01-01-2022 ∧ Post.PostedBy=1 (πTopic,WhenPosted,PostedBy(Post × Forum))) Note: The exact syntax may v......Login to view full explanation

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