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.
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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 on a foreign key of r referencing s, where the foreign
key attribute is declared to be not null.
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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 not on a foreign key.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.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?
- 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).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?What does an EXCEPT (MINUS) query care about operand order, while a UNION query doesn't?
- 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.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.Find a SQL query that computes a set difference and returns false positive(s) over a database with null values. You may show the correctness of your answer using an example.
- 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?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.Consider the query:select *from r, swhere upper(r.A) = upper(s.A);where “upper” is a function that returns its input argument with all lowercaseletters replaced by the corresponding uppercase letters. Find out what plan is generated for this query on the database system you use.