Suppose you want to get answers to r ⋈ s sorted on an attribute of r, andwant only the top K answers for some relatively small K. Give a good way ofevaluating the query:When the join is not on a foreign key.
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Suppose you want to get answers to r ⋈ s sorted on an attribute of r, and
want only the top K answers for some relatively small K. Give a good way of
evaluating the query:
When the join is not on a foreign key.
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- Suppose you want to get answers to r ⋈ s sorted on an attribute of r, andwant only the top K answers for some relatively small K. Give a good way ofevaluating the query:When the join is on a foreign key of r referencing s, where the foreign key attribute is declared to be not null.Consider the queryselect A, Bfrom rwhere r.B < some (select Bfrom swhere s.A = r.A)Show how to decorrelate this query using the multiset version of the semi joinoperation.Consider the following SQL Query: SELECT FNAME, DNAME FROM EMP AS E, DEPT AS D WHERE E.DNO = D.DNUMBER AND D.DNAME='CCI' AND SALARY > 15000; Draw the initial query tree for the above SQL query, and then show how the query tree is optimized by applying the Heuristic Rules. (You need to show the tree after applying a rule).
- Give pseudocode for computing a join: r ⋈r.A=s.A s using a single MapReduce step, assuming that the map() function is invoked on each tuple of r and s. Assume that the map() function can find the name of the relation using context.relname().When a relation is partitioned on one of its properties by: a. Hash partitioning, what factors could cause skew? What about range partitioning? What can be done in each scenario to lessen the skew?a. What is the result of this query:SELECT AVG (S.rating)FROM Sailors S b. What is the result of this query:SELECT COUNT (S.rating)FROM Sailors S c. Show the full outer join of S with itself, with the join condition being sid=sid .
- But why does the order of operands matter for UNION queries but not for EXCEPT (MINUS) searches?Given the tables create table T (A int primary key, B int); create table U (C int primary key, A int, foreign key(A) references T(A) ); Table T contains 100 rows and table U contains 200 rows. A common mistake made by students is to do a join and assuming the database will supply the join predicate. A student does the query SELECT T.A, T.B, U.C FROM T, U; The student does not get an error message but gets a large result set. How many rows are in the result set?You have the table T = (name, ssn, phone number) representing a person. Each name is uniquely identified by ssn, but the same name can have multiple phone numbers. Suppose you break the tables into two tables T1=(name, ssn) and T2= (name, phone number) a) What are the candidate keys of T, T1, and T2, respectively?
- Suppose an application programmer was supposed to write a query select * from r natural left outer join s; on relations r(A, B) and s(B, C), but instead wrote the query select * from r natural join s; a. Give sample data for r and s on which both queries would give the same result. b. Give sample data for r and s where the two queries would give different results, thereby exposing the error in the query.Modify the recursive query in Figure 5.16 to define a relationprereq_depth(course_id, prereq_id, depth) where the attribute depth indicates how many levels of intermediate prerequisites there are between the course and the prerequisite. Direct prerequisites havea depth of 0. Note that a prerequisite course may have multiple depths and thusmay appear more than once.Thus, persons are represented as pairs of integers: e = (birth, size), where the first number represents the date of birth of the person and the second his leg size. Date of birth is key. Describe how to expand the data structure of the skip list to respond effectively to the query: Max (d1, d2), which returns the date of birth of the person with the largest leg and born between dates d1 and d2.