DBMS & SQL Previous Year Questions

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Bundling data and the functions that work on it into one unit is encapsulation.

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A database is an organised collection of data that can be accessed, updated and managed.

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A database can hold images, text/files and audio or video data, so more than one option is correct.

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Microsoft Access and IBM Db2 are DBMS products; Google is a search engine company, not a DBMS.

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A DBMS supports many users at once, so 'single-user access only' is not a feature.

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Databases manipulate and secure data; analysing code is not a database function.

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A DBMS sits between the database applications (users' programs) and the stored database.

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A superkey is any set of attributes that together uniquely identify a record.

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'DELETE FROM teaches;' removes all rows (values) of the relation; the other forms are wrong or remove different things.

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The HAVING clause filters groups after GROUP BY and may use aggregate functions.

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Only III (process organization) is not a DBMS utility, but none of the options A-C lists exactly that, so the answer is None of the above.

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Third normal form (3NF) is generally considered adequate for a normal relational design.

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A truth table with n inputs has 2ⁿ rows, so 4 inputs give 2⁴ = 16 rows.

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An 8-to-1 multiplexer needs n select lines where 2ⁿ = 8, so n = 3.

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A hash table supports search, insertion and deletion in O(1) average time. A stack or queue only gives access at its ends.

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Array elements sit in contiguous memory, so any element can be accessed directly by its index in O(1). Insertion and deletion cost O(n), and the elements must all be the same type.

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Relational, object-oriented, hierarchical and network are types of DBMS. "Sequential" describes a file organisation, not a DBMS model.

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A primary key uniquely identifies each record (row) in a table and cannot be NULL. Linking tables is the job of a foreign key.

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2NF requires 1NF and that every non-prime attribute depend fully on the whole primary key, with no partial dependency on part of a composite key.

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INSERT INTO table VALUES (...) adds new rows. CREATE makes database objects such as tables.

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Copies of the same data at several sites can get out of sync, which causes data inconsistency. Better data accessibility is an advantage.

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All three statements are true: a compiler takes the source program as input, translates the whole of it at once, and produces object code as output.

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In ADD X Y the operands are given by their memory addresses X and Y, which is absolute (direct) addressing.

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A view is a virtual table, the stored result of a query. It does not hold its own data and is built from the base tables when used.

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A table can have only one primary key, although that key may be made of several columns (a composite key).

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UNION is a set operator that combines the results of queries. PRIMARY KEY and NOT NULL are constraints.

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ORDER BY sorts in ascending (ASC) order by default.

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HAVING filters groups made by GROUP BY, while WHERE filters individual rows before they are grouped.

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The WITH clause (a common table expression) defines a temporary named relation that exists only for that query.

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ROUND(65.726, −1) rounds to the nearest ten, because a negative position counts left of the decimal point, so 65.726 becomes 70.

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COMMIT makes the changes made by a transaction permanent. ROLLBACK undoes them, and TRUNCATE removes all rows from a table.

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Tables can be joined with join operations such as natural join and union join, or by using subqueries, so more than one option applies.

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Array elements are stored next to each other, so any element can be reached directly by its index in O(1) time. Arrays hold only one data type, and indexing starts at 0.

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With this convention, front and rear start at −1. Front = rear = −1 means the queue is empty, and front = rear ≥ 0 means it holds one element.

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A DBMS supports access by many users at once (concurrency control). Single-user-only access is not a DBMS feature.

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Referential integrity requires every foreign key value in the referencing relation to appear as a key value in the referenced relation.

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The partition table in the MBR describes where each partition lies on the disk. If it is corrupted, the system cannot find any partition, so the whole disk becomes inaccessible.

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A foreign key is an attribute in one table that refers to the primary key of another table. It links the two tables and enforces referential integrity.

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2NF requires 1NF plus full functional dependency of every non-key attribute on the whole primary key, so there are no partial dependencies.

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A domain is the set of allowed values, or data type, for an attribute (column) in a relation.

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Degree is the number of attributes (columns) in a relation. Cardinality is the number of tuples (rows).

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UPDATE changes the values of existing rows, for example UPDATE t SET col = val WHERE .... INSERT adds rows and ALTER changes the table structure.

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SELECT retrieves (queries) data from one or more tables. DISPLAY and SHOW are not standard SQL query commands.

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ALTER TABLE changes a table's structure, for example to add, drop or modify columns. UPDATE changes data, not structure.

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LIKE matches patterns using the wildcards % (any sequence) and _ (one character). IN tests a list and BETWEEN tests a range.

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Degree (attributes) becomes 4 + 3 = 7 and cardinality (tuples) becomes 3 + 4 = 7, so both are 7.

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DROP TABLE removes the whole table, structure and data. DELETE removes only rows, and ERASE is not an SQL command.

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The memory address register (MAR) holds the address of the memory location being read or written. The memory buffer register (MBR) holds the data itself.