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web.groovymark@gmail.com
- October 25, 2024
Question 21
In database design, what does a composite primary key consist of?
a) A single column
b) Multiple columns
c) A combination of primary and foreign keys
d) Two foreign keys
Correct Answer: b) Multiple columns
Explanation: A composite primary key is made up of two or more columns in a table, and together these columns uniquely identify each row.
Question 22
Which type of join includes all rows from the left and right tables, regardless of whether they have matches?
a) INNER JOIN
b) FULL JOIN
c) LEFT JOIN
d) RIGHT JOIN
Correct Answer: b) FULL JOIN
Explanation: A FULL JOIN selects all rows from both tables, regardless of whether there is a match, filling in NULLs where necessary.
Question 23
Which type of index is used in SQL databases to assign entries to buckets?
a) Sparse Index
b) Hash Index
c) Bitmap Index
d) Dense Index
Correct Answer: b) Hash Index
Explanation: A Hash Index assigns index entries to buckets using a hash function, which computes a bucket number from the value of the indexed column.
Question 24
What does the SQL clause GROUP BY do?
a) Orders the results by a specified column
b) Filters the results based on a condition
c) Groups rows that have the same values in specified columns
d) Joins two or more tables based on a condition
Correct Answer: c) Groups rows that have the same values in specified columns
Explanation: The GROUP BY clause groups rows that have the same values in specified columns, often used with aggregate functions like SUM() or COUNT(). EQUIJOIN is used to compare columns using the = operator in SQL. It is the most common type of join where two tables are joined based on equality between specified columns.
Question 25
Which command in SQL deletes a table from a database entirely, including all rows and structure?
a) DELETE
b) TRUNCATE
c) DROP TABLE
d) REMOVE TABLE
Correct Answer: c) DROP TABLE
Explanation: The DROP TABLE command removes an entire table, including its rows and structure, from the database.
Question 26
In SQL, which operator is used for pattern matching with wildcards?
a) LIKE
b) IN
c) BETWEEN
d) EXISTS
Correct Answer: a) LIKE
Explanation: The LIKE operator is used for pattern matching in SQL, often with wildcard characters such as '%' for multiple characters or '_' for a single character.
Question 27
Which SQL statement is used to change the data in an existing row in a table?
a) INSERT
b) UPDATE
c) DELETE
d) CREATE
Correct Answer: b) UPDATE
Explanation: The UPDATE statement is used to modify the data in existing rows in a table by specifying new values for the columns.
Question 28
Which SQL command is used to create an index on one or more columns of a table?
a) CREATE INDEX
b) ALTER TABLE
c) CREATE TABLE
d) CREATE VIEW
Correct Answer: a) CREATE INDEX
Explanation: The CREATE INDEX command creates an index on one or more columns of a table to improve the speed of data retrieval operations.
Question 29
Which clause in SQL is used to limit the number of rows returned by a SELECT statement?
a) WHERE
b) HAVING
c) LIMIT
d) ORDER BY
Correct Answer: c) LIMIT
Explanation: The LIMIT clause is used to specify the maximum number of rows to be returned by a SELECT query, limiting the result set.
Question 30
In a relational database, what does the term “schema” refer to?
a) The structure of a database, including tables, columns, and relationships
b) A subset of data in a table
c) A specific row in a table
d) A command to retrieve data from a table
Correct Answer: a) The structure of a database, including tables, columns, and relationships
Explanation: The schema of a database defines its structure, including the tables, columns, data types, and relationships between tables. established when a foreign key in one table refers to the primary key in another table, allowing multiple rows in the first table to relate to a single row in the second.
Question 31
Which SQL operator is used to return unique values from a column?
a) DISTINCT
b) UNIQUE
c) LIKE
d) BETWEEN
Correct Answer: a) DISTINCT
Explanation: The DISTINCT operator returns only unique values from a column, removing any duplicate values from the result set.
Question 32
Which type of key in a table is used to refer to the primary key in another table?
a) Foreign Key
b) Composite Key
c) Primary Key
d) Unique Key
Correct Answer: a) Foreign Key
Explanation: A Foreign Key is used to refer to the primary key in another table, establishing a relationship between the two tables.
Question 33
What is the purpose of a CHECK constraint in SQL?
a) To ensure that values in a column follow a specific rule
b) To create a relationship between two tables
c) To remove duplicate rows from a result set
d) To limit the number of rows returned by a query
Correct Answer: a) To ensure that values in a column follow a specific rule
Explanation: A CHECK constraint ensures that values in a column must satisfy a specified condition or rule, enforcing data integrity.
Question 34
In which normal form is a table if all columns are functionally dependent on the primary key, and there are no transitive dependencies?
a) First Normal Form (1NF)
b) Second Normal Form (2NF)
c) Third Normal Form (3NF)
d) Boyce-Codd Normal Form (BCNF)
Correct Answer: c) Third Normal Form (3NF)
Explanation: A table is in Third Normal Form (3NF) when all columns are functionally dependent on the primary key and there are no transitive dependencies between non-key columns.
Question 35
Which SQL statement is used to delete specific rows from a table based on a condition?
a) DELETE
b) TRUNCATE
c) DROP TABLE
d) UPDATE
Correct Answer: a) DELETE
Explanation: The DELETE statement is used to remove specific rows from a table based on a condition specified in the WHERE clause.
Question 36
Which clause in SQL is used to filter rows before grouping them in a GROUP BY query?
a) HAVING
b) WHERE
c) LIMIT
d) ORDER BY
Correct Answer: b) WHERE
Explanation: The WHERE clause filters rows before they are grouped in a GROUP BY query, applying conditions to individual rows.
Question 37
Which type of key uniquely identifies each row in a table and must always contain unique, non-null values?
a) Primary Key
b) Foreign Key
c) Composite Key
d) Unique Key
Correct Answer: a) Primary Key
Explanation: The Primary Key uniquely identifies each row in a table and ensures that no two rows have the same value in the primary key column(s).
Question 38
What is the main purpose of the ALTER TABLE command in SQL?
a) To modify the structure of an existing table
b) To delete all rows from a table
c) To add rows to a table
d) To create a new index on a table
Correct Answer: a) To modify the structure of an existing table
Explanation: The ALTER TABLE command is used to change the structure of an existing table, such as adding, removing, or modifying columns.
Question 39
Which type of join includes all rows from the right table and only matching rows from the left table?
a) LEFT JOIN
b) INNER JOIN
c) RIGHT JOIN
d) FULL JOIN
Correct Answer: c) RIGHT JOIN
Explanation: A RIGHT JOIN includes all rows from the right table and only the matching rows from the left table. Rows from the right table without a match in the left table will still appear in the result.
Question 40
Which term describes the dependence of one column on another in a table, where one value determines another?
a) Functional Dependence
b) Composite Key
c) Foreign Key
d) Index
Correct Answer: a) Functional Dependence
Explanation: Functional Dependence occurs when one column's value is determined by another column's value in a database table.
