DBMS & SQL Previous Year Questions (page 4)

Explanation

The aggregate function MIN() returns the smallest value in a column. LOWEST() does not exist, and an aggregate cannot be used directly in a WHERE clause.

Explanation

To compare each student with their own department's average, the subquery must be correlated: WHERE dept_id = s.dept_id links it to the outer row. Option A's subquery returns several averages, and B uses an aggregate in WHERE, which is not allowed.

Explanation

A page table holds, for each page of a process, the frame number in physical memory, so it translates virtual (logical) addresses into physical addresses. It holds no process data or instructions.

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File permissions (for example read, write and execute for owner, group and others in Unix) control who may access a file and in what way.

Explanation

COMMIT ends a transaction and makes all its changes permanent in the database. ROLLBACK is the command that undoes them.

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SELECT is the privilege that allows reading rows from a table, so GRANT SELECT ON Customers TO Deepak; is correct. READ and ACCESS are not SQL privileges, and GIVE is not an SQL command.

Explanation

Client-side JavaScript runs inside the user's web browser, where it handles events, checks forms and updates the page without going to the server.

Explanation

The dual aspect concept says every transaction has two equal effects, a debit and a credit, which is the basis of the equation Assets = Liabilities + Capital.

Explanation

Standard SQL supports -- for single-line (and end-of-line) comments and /* ... */ for block comments. // is a comment in C++/Java/JavaScript, not in SQL-99.

Explanation

Standard SQL requires the keyword INTO in an INSERT statement: INSERT INTO table VALUES (...). Omitting INTO is only accepted by some vendors such as MySQL or SQL Server, so D is invalid in standard SQL.

Explanation

An OR gate gives 0 only when all inputs are 0. So A = 0, B = 0 gives Y = 0, and the statement Y = 1 is incorrect.

Explanation

WITH CHECK OPTION rejects any INSERT or UPDATE through the view that would produce a row not satisfying the view's WHERE condition (a row that would vanish from the view).

Explanation

CREATE TABLE new_table AS SELECT * FROM old_table creates the new table and copies all rows of the old one into it. CREATE, UPDATE or INSERT cannot follow AS here.

Explanation

Inserting 45 at index 4 shifts 50 and 60 one place right, giving [10, 20, 30, 40, 45, 50, 60]. The other options contain 25, which was never in the array.

Explanation

R2 - 2R1 gives [0, -2, 2, 6] and R3 - 4R1 gives [0, -3, 3, 9], which is 1.5 times the new R2, so one row becomes zero. The rank is 2, so the normal form is [I2 0; 0 0].

Explanation

Goods taken for personal use reduce the goods available for sale, so the entry is Drawings A/c Dr. to Purchases A/c (at cost). No cash is involved.

Explanation

P is true (lists grow and shrink at run time) and R is true (nodes are allocated only when needed). Q is false: linked lists need O(n) traversal to reach an index; arrays give constant-time indexed access.

Explanation

A compiler is system software (a language translator) that supports program development. DBMS, web browsers and word processors are application software.

Explanation

Any ordinary comparison involving NULL (=, <=, >= etc.) gives UNKNOWN, not TRUE. The IS NULL predicate is the special test for nulls, so NULL IS NULL is TRUE.

Explanation

The schema is the overall logical design (structure) of the database, which rarely changes. An instance is the data stored in the database at a particular moment.

Explanation

A view is a virtual table, and standard SQL (SQL:1999) does not allow ORDER BY in the view's defining query; ordering is applied when the view is queried. Subqueries and aggregates are allowed.

Explanation

To insert values into only some columns, list those columns after the table name and give matching values: INSERT INTO table (cols) VALUES (...). Option B gives no column list, so it expects values for all columns.

Explanation

UPDATE ... SET ... WHERE ... is the DML command that changes existing rows. SET is only a clause of UPDATE, and MODIFY is used with ALTER TABLE in some systems.

Explanation

Each step compares with the middle element and discards half the array, so T(n) = T(n/2) + O(1), giving O(log n) in the worst case. The best case is O(1) and the average case is O(log n), and the recurrence has T(n/2) once, not twice.

Explanation

The instruction cycle consists of fetch, decode, execute (and store/write-back of results). "Encode" is not a phase; the correct step is decode.

Explanation

EPROM (Erasable PROM) is erased by exposing its quartz window to ultraviolet light. EEPROM and flash are erased electrically, and PROM cannot be erased.

Explanation

!= (not equal to) is a relational operator. && and || are logical AND/OR, and ! is logical NOT.

Explanation

Front-end development tools help developers build attractive website layouts and user interfaces quickly. Back-end tools deal with servers and databases.

Explanation

In a DTD an element is declared as <!ELEMENT element-name category>. <!ATTLIST> declares attributes and <!ENTITY> declares entities.

Explanation

JavaScript runs in the browser and is used to build the front end. PHP and Django are server-side, and SQL is for databases.

Explanation

The cycle is: transactions → journal → ledger → trial balance → adjustment entries → adjusted trial balance → closing entries → financial statements, as in (B).

Explanation

The DEFAULT constraint supplies a default value for a column when no value is given in an INSERT. NOT NULL, CHECK and UNIQUE do the other jobs.

Explanation

A group of RadioButtons lets the user choose exactly one option from several choices.

Explanation

A variable is a symbolic name for a memory location whose value can change while the program runs.

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A Management Information System is a planned system for collecting, storing and sharing information that managers need to do their work.

Explanation

A try block can be followed by many catch blocks but at most one finally block. A try with only a finally (no catch) is also allowed, so A is wrong.

Explanation

Under the double-entry system, every transaction has two aspects, a debit and a credit, of equal amounts.

Explanation

PQ⁺: P → RT adds R and T, and Q → S adds S. QS → TU then adds U, so PQ⁺ = PQRSTU (PQ is a key).

Explanation

GETDATE() in SQL Server returns the current database system timestamp as a datetime value without the time zone offset.

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A primary index is an ordered file of fixed-length records with two fields: the primary key value and a pointer to the disk block holding that record.

Explanation

Since a = 20 and b = 35, the condition a >= b is False, so the else branch runs and prints "No".

Explanation

ord() converts a character to its integer Unicode code, e.g. ord("A") = 65. tuple(), dict() and set() build collections.

Explanation

DATEDIFF returns the difference between startdate and enddate in the given datepart, so I is correct. The datepart cannot be supplied through a user-defined variable or quoted string, so II is wrong.

Explanation

append() adds a single element to the end of a list. pop() removes an element, sort() orders the list, index() finds a position.

Explanation

print() of a tuple shows its repr: parentheses, with strings in single quotes, so the output is ('Example', 1, 'Tuple').

Explanation

A weak entity is drawn as a double rectangle (option C). A single rectangle is a strong entity, a diamond a relationship, and a double diamond an identifying relationship.

Explanation

VLINK sets the colour of visited links (those already clicked). LINK is for unvisited links and ALINK for the active link while it is being clicked.

Explanation

First Normal Form requires atomic attribute values, so it disallows nested relations or relations as attribute values within tuples.