Consider a database that has the relation schemas EMP(EmpId, EmpName, DeptId), and DEPT(DeptName, DeptId). Note that the DeptId can be permitted to be NULL in the relation EMP. Consider the following queries on the database expressed in tuple relational calculus. (I) {t | u EMP(t[EmpName] = u[EmpName] v DEPT(t[DeptId] v[DeptId]))} (II) {t | u EMP(t[EmpName] = u[EmpName] v DEPT(t[DeptId] v[DeptId]))} (III) {t | u EMP(t[EmpName] = u[EmpName] v DEPT(t[DeptId] = v[DeptId]))} Which of the above queries are safe?

Consider a database that has the relation schemas EMP(EmpId, EmpName,

1.	Consider a database that has the relation schemas EMP(EmpId, EmpName, DeptId), and DEPT(DeptName, DeptId). Note that the DeptId can be permitted to be NULL in the relation EMP. Consider the following queries on the database expressed in tuple relational calculus. (I) {t \| u EMP(t[EmpName] = u[EmpName] v DEPT(t[DeptId] v[DeptId]))} (II) {t \| u EMP(t[EmpName] = u[EmpName] v DEPT(t[DeptId] v[DeptId]))} (III) {t \| u EMP(t[EmpName] = u[EmpName] v DEPT(t[DeptId] = v[DeptId]))} Which of the above queries are safe?
A.	(I) and (II) only
B.	(I) and (III) only
C.	(II) and (III) only
D.	(I), (II) and (III)
Answer» E.

Discussion

No Comment Found

Related MCQs

Which of the following statements are true about an SQL query? P. An SQL query can contain HAVING clause even if it does not have a GROUP BY clause Q. An SQL query can contain HAVING clause only if it does not have a 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
Consider the following log sequence of two transactions on a bank account, with initial balance 12000, that transfer 2000 to a mortagage payment and then apply a 5% interest. 1. T1 start 2. T1 B old = 1200 new = 10000 3. T1 M old = 0 new = 2000 4. T1 commit 5. T1 start 6. T2 B old = 10000 new = 10500 7. T2 commit Suppose the database system crashes just before log record is written. When the system is started, which one statement is true of the recovery procedure?
Which of the following concurrency control protocols ensure both conflict serializability and freedom from deadlock ? 1. 2-phase locking 2. Time-stamp ordering
Consider the following transactions with data items P and Q initialized to zero : T1 : read (P); read (Q); if P = 0 then Q = Q + 1; write (Q); T2 : read (Q); read (P); if Q = 0 then P = P + 1; write (P); Any non-serial interleaving of T1 and T2 for concurrent execution leads to
Consider the transactions T1, T2, and T3 and the schedules S1 and S2 given below. T1: r1(X); r1(Z); w1(X); w1(Z) T2: r2(Y); r2(Z); w2(Z) T3: r3(Y); r3(X); w3(Y) S1: r1(X); r3(Y); r3(X); r2(Y); r2(Z); w3(Y); w2(Z); r1(Z); w1(X); w1(Z) S2: r1(X); r3(Y); r2(Y); r3(X); r1(Z); r2(Z); w3(Y); w1(X); w2(Z); w1(Z) Which one of the following statements about the schedules is TRUE ?
Consider a simple checkpointing protocol and the following set of operations in the log. (start, T4); (write, T4, y, 2, 3); (start, T1); (commit, T4); (write, T1, z, 5, 7); (checkpoint); (start, T2); (write, T2, x, 1, 9); (commit, T2); (start, T3), (write, T3, z, 7, 2); If a crash happens now the system tries to recover using both undo and redo operations, what are the contents of the undo list and the redo list?
Consider the following transaction involving two bank accounts x and y. read(x); x: = x 50; write(x); read (y); y = y + 50; write(y) The constraint that the sum of the accounts x and y should remain constant is that of
Consider the following database schedule with two transactions, T1 and T2. S = r2 (X); r1(X); r2 (Y); w1 (X); r1 (Y); w2 (X); a1; a2 where ri (Z) denotes a read operation by transaction Ti on a variable Z, wi (Z) denotes a write operation by Ti on a variable Z and ai denotes an abort by transaction Ti. Which one of the following statements about the above schedule is TRUE ?
Suppose a database schedule S involves transactions T1, ...., Tn. Construct the precedence graph of S with vertices representing the transactions and edges representing the conflicts. If S is serializable, which one of the following orderings of the vertices of the precedence graph is guaranteed to yield a serial schedule?
Consider the following database table named top_scorer. <table class="wp-block-table"><tbody><tr><td>Player </td><td> Country </td><td> Goals </td></tr><tr><td>Klose </td><td>Germany </td><td>16 </td></tr><tr><td>Ronaldo </td><td>Brazil </td><td>15 </td></tr><tr><td>G Muller </td><td>Gemany </td><td>14 </td></tr><tr><td>Fontaine </td><td>France </td><td>13 </td></tr><tr><td>Pele </td><td> Brazil </td><td>12 </td></tr><tr><td>Klinsmann </td><td> Germany </td><td>11 </td></tr><tr><td>Kocsis </td><td>Hungary </td><td>11 </td></tr><tr><td>Batistuta </td><td>Argentina </td><td>10 </td></tr><tr><td>Cubillas </td><td> Peru </td><td>10 </td></tr><tr><td>Lato </td><td>Poland </td><td>10 </td></tr><tr><td>Lineker </td><td>England </td><td>10 </td></tr><tr><td>T Miller </td><td>Germany </td><td>10 </td></tr><tr><td>Rahn </td><td>Germany </td><td>10 </td></tr></tbody></table> Consider the following SQL query: SELECT ta.player FROM top_scorer AS ta WHERE ta.goals >ALL (SELECT tb.goals FROM top_scorer AS tb WHERE tb.country = Spain ) AND ta.goals >ANY (SELECT tc.goals FROM top_scorer AS tc WHERE tc.country = Germany ) The number of tuples returned by the above SQL query is ________.

Discussion

No Comment Found

Related MCQs

Reply to Comment