Aquery processoris responsible forquery optimization and executionin a database management system (DBMS). It analyzes SQL statements, optimizes execution plans, and ensures efficient retrieval of data.
Option A (Correct):Thequery processoroptimizes queries by analyzing metadata from thesystem catalogto determine the best execution strategy.
Option B (Incorrect):Logging transactionsbefore applying changes is the responsibility of thetransaction manager.
Option C (Incorrect):Translating instructions intofile system commandsis handled by thestorage manager, not the query processor.
Option D (Incorrect):While the query processor helps retrieve results, thedatabaseengineandAPI layerare responsible for returning results to applications.
[Reference:Query optimization and execution in relational databases., ]
Question 2
How can a primary key constraint be added after the table is created?
Options:
A.
By using an ALTER clause
B.
By using the CREATE TABLE statement
C.
By using an UPDATE clause
D.
By using an INSERT INTO clause
Answer:
A
Explanation:
Toadd a primary key constraint after table creation, we use theALTER TABLEstatement.
Example Usage:
sql
ALTER TABLE Employees
ADD CONSTRAINT PK_Employees PRIMARY KEY (EmpID);
Thisaddsa primary key to the EmpID columnafter the table was created.
Why Other Options Are Incorrect:
Option B (CREATE TABLE) (Incorrect):Used for defining constraintsduringtable creation, not after.
Option C (UPDATE) (Incorrect):Modifiesrow values, not constraints.
Option D (INSERT INTO) (Incorrect):Used toadd datato a table, not modify constraints.
Thus, the correct answer isALTER TABLE, as itmodifies table structure to add a primary key constraint.
[Reference:SQL ALTER TABLE and Constraints., ]
Question 3
What does the aggregate function do?
Options:
A.
It computes values over a set of rows.
B.
It selects rows that appear in one table but not another.
C.
It eliminates one or more columns of a table.
D.
It lists combinations of rows in two tables.
Answer:
A
Explanation:
Anaggregate functionperforms acalculation over multiple rowsand returns asingle value. Examples includeSUM(), AVG(), MAX(), MIN(), and COUNT()in SQL.
Option A (Correct):Aggregate functions compute values over aset of rows, like summingtotal sales or averaging grades.
Option B (Incorrect):Selecting rows that appear in one table but not another is done usingset operations (EXCEPT or MINUS in SQL).
Option C (Incorrect):Eliminating columns is done using thePROJECToperation orSELECT with specific columns.
Option D (Incorrect):Combining rows from two tables refers to aJOIN operation, not aggregation.
[Reference:Aggregate functions in relational algebra., , , ]