Consider the nested query we saw in section 1344

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Consider the nested query we saw in Section 13.4.4 which finds the names of all instructors who taught a course in 2007. Write the query in relational algebra using the multiset semjoin operation, ensuring that the number of duplicates of each name is the same as in the SQL query. (The semijoin operation is widely used for decorrelation of nested queries.) Answer: The query can be written as follows: instructor instructor . I D = teaches . I D ( H9268 year = 2007 ( teaches ))
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