Database Management System MCQs

Which of the following scenarios may lead to an irrecoverable error in a database system?

Which one of the following is a key factor for preferring B+-trees to binary search trees for indexing database relations?

Consider three data items D1, D2, and D3, and the following execution schedule of transactions T1, T2, and T3. In the diagram, R(D) and W(D) denote the actions reading and writing the data item D respectively.

Which of the following statements is correct?

Which of the following satements are TRUE about an SQL query?(GATE-2012)

P: An SQL query can contain a HAVING clause even if it does not have a GROUP BY clause.

Q: An SQL query can contain a HAVING clause only if it has GROUP BY clause

R: All attributes used in the GROUP BY clause must appear in the SELECT clause.

S: Not all attributes used in the GROUP BY clause need to appear in the SELECT clause.

Let E1 and E2 be two entities in an E/R diagram with simple single-valued attributes. R1 and R2 are two relationships between E1 and E2, where R1 is one-tomany and R2 is many-to-many. R1 and R2 do not have any attributes of their own. What is the minimum number of tables required to represent this situation in the relational model?