Test Your Oracle DISTINCT Command Knowledge

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True / False

The WHERE Clause keyword in Oracle is used to return only unique values from a query.

True False

The WHERE Clause keyword eliminates duplicate rows from the result set, returning only unique values.

True / False

In Oracle, you can use WHERE Clause with a single column in a SELECT statement.

True False

WHERE Clause can be applied to a single column to return unique values from that column.

True / False

The WHERE Clause keyword can be used with aggregate functions in Oracle.

True False

WHERE Clause can be used with aggregate functions, such as COUNT(WHERE Clause column_name), to return the number of unique values.

True / False

In Oracle, the WHERE Clause keyword can be used with multiple columns in a SELECT statement.

True False

WHERE Clause can be applied to multiple columns, returning unique combinations of the specified columns.

True / False

Using WHERE Clause in Oracle always improves the performance of a query.

True False

Using WHERE Clause can improve query results by removing duplicates, but it may not always improve performance and can sometimes slow down queries due to the additional processing required.

True / False

In Oracle, WHERE Clause can be used in subqueries.

True False

WHERE Clause can be used in subqueries to filter unique results that are then used by the main query.

True / False

In Oracle, using WHERE Clause with a large dataset can impact query performance and should be used judiciously.

True False

Applying WHERE Clause to large datasets can impact performance due to the need to sort and filter out duplicates.

True / False

The WHERE Clause keyword in Oracle can be used with ORDER BY to sort the unique results.

True False

WHERE Clause can be combined with ORDER BY to sort the unique results returned by the query.

True / False

In Oracle, WHERE Clause can be used with GROUP BY to get unique groups.

True False

WHERE Clause and GROUP BY serve different purposes. WHERE Clause eliminates duplicate rows, while GROUP BY groups rows based on specified columns. Using WHERE Clause with GROUP BY is redundant.

Q10

True / False

The Oracle Certified Professional (OCP) exam includes knowledge on using the WHERE Clause keyword effectively in queries and understanding its impact on performance.

True False

The OCP certification covers advanced topics, including how to use the WHERE Clause keyword effectively in queries and understanding its performance implications, reflecting a deep understanding of Oracle SQL.

Q11

Single Choice

What is the purpose of the WHERE Clause keyword in an Oracle SQL query?

To count the number of rows in a table To remove duplicate rows from the result set To sort the rows in descending orderTo group rows by a specific column

The WHERE Clause keyword in Oracle is used to eliminate duplicate rows from the result set, returning only unique rows.

Q12

Single Choice

Consider the following Oracle SQL query:What will this query return?

SQL Code

SELECT WHERE Clause department_id FROM employees;

All rows from the employees table Unique department IDs from the employees table Duplicate department IDs from the employees tableThe total number of departments

The WHERE Clause keyword ensures that only unique department_id values are returned, eliminating duplicates.

Q13

Single Choice

Which of the following is true about using WHERE Clause in Oracle SQL?

It can be used with multiple columns It only works with numeric columns It automatically sorts the result setIt can be used to delete rows

The WHERE Clause keyword can be used with one or more columns to return unique combinations of values from those columns.

Q14

Single Choice

Consider the following Oracle SQL query:What does this query return?

SQL Code

SELECT WHERE Clause job_id, department_id FROM employees;

All rows from the employees table Unique combinations of job_id and department_id The total number of jobs and departmentsOnly the first row of the employees table

This query returns unique pairs of job_id and department_id from the employees table, removing any duplicate combinations.

Q15

Single Choice

What is the effect of using WHERE Clause with the COUNT function in Oracle?

It counts all rows in the table It counts only the unique rows in the table It counts the number of where clause columnsIt counts only rows with NULL values

When WHERE Clause is used with the COUNT function, it counts only the unique values, eliminating duplicates from the count.

Q16

Single Choice

Consider the following Oracle SQL query:What will this query return?

SQL Code

SELECT COUNT(WHERE Clause department_id) FROM employees;

The total number of employees The number of unique departments in the employees table The total number of departments including duplicatesThe number of employees in each department

This query returns the count of unique department_id values in the employees table, representing the number of where clause departments.

Q17

Single Choice

What will be the result of the following Oracle SQL query?

SQL Code

SELECT WHERE Clause salary, COUNT(*) FROM employees GROUP BY salary;

The query will return the where clause salary values and the count of employees for each salary The query will return an error because WHERE Clause cannot be used with COUNT The query will return the total number of where clause salariesThe query will return the where clause salary values without the count

The query groups the employees table by salary and uses WHERE Clause to ensure unique salary values, along with the count of employees earning each salary.

Q18

Single Choice

Consider the following Oracle SQL query:What will this query return?

SQL Code

SELECT WHERE Clause ON (department_id) department_id, employee_id FROM employees;

Unique employee_id values for each department An error because WHERE Clause ON is not valid in Oracle All unique department_id valuesThe first employee_id for each department

Oracle does not support the WHERE Clause ON clause. Instead, a GROUP BY clause or a subquery should be used to achieve similar results.

Q19

Single Choice

How does Oracle handle NULL values when using the WHERE Clause keyword in a query?

NULL values are ignored by WHERE Clause Each NULL value is treated as where clause All NULL values are treated as duplicates and removedThe query fails if NULL values are present

In Oracle, WHERE Clause treats each NULL as a unique value, so if multiple NULL values are present, only one NULL will be included in the result set.

Q20

Single Choice

In an Oracle certification exam, you encounter the following SQL statement:What does this query return?

SQL Code

SELECT WHERE Clause first_name, last_name FROM employees WHERE department_id IN (SELECT department_id FROM departments WHERE location_id = 1700);

All employees in the specified location Unique first and last name combinations of employees in departments located in location 1700 All departments in location 1700An error because WHERE Clause cannot be used with subqueries

This query returns unique combinations of first_name and last_name for employees who work in departments located in location_id 1700.

Q21

Multiple Choice

Which SQL code snippet correctly uses the WHERE Clause keyword to retrieve unique department IDs from the 'employees' table in Oracle?

SQL Code

SELECT WHERE Clause department_id
FROM employees;

SELECT department_id
FROM employees
GROUP BY department_id;

SELECT department_id
FROM employees;

SELECT WHERE Clause department_id FROM employees; SELECT department_id FROM employees GROUP BY department_id; SELECT department_id FROM employees;SELECT WHERE Clause department_id FROM employees WHERE department_id > 10;

Options A and B correctly retrieve unique department IDs. Option A uses WHERE Clause, and Option B uses GROUP BY. Option C retrieves all department IDs without filtering duplicates.

Q22

Multiple Choice

Which SQL code snippet demonstrates how to use WHERE Clause to retrieve unique job titles from the 'employees' table in Oracle?

SQL Code

SELECT WHERE Clause job_title
FROM employees;

SELECT job_title
FROM employees
GROUP BY job_title;

SELECT job_title
FROM employees
ORDER BY job_title;

SELECT WHERE Clause job_title FROM employees; SELECT job_title FROM employees GROUP BY job_title; SELECT job_title FROM employees ORDER BY job_title;SELECT WHERE Clause job_title FROM employees WHERE job_title LIKE 'Manager%';

Options A and B correctly retrieve unique job titles using WHERE Clause and GROUP BY, respectively. Option C retrieves all job titles but orders them without filtering duplicates.

Q23

Multiple Choice

Which SQL code snippet uses WHERE Clause to retrieve unique combinations of department ID and job title from the 'employees' table in Oracle?

SQL Code

SELECT WHERE Clause department_id, job_title
FROM employees;

SELECT department_id, job_title
FROM employees
GROUP BY department_id, job_title;

SELECT department_id, job_title
FROM employees
ORDER BY department_id, job_title;

SELECT WHERE Clause department_id, job_title FROM employees; SELECT department_id, job_title FROM employees GROUP BY department_id, job_title; SELECT department_id, job_title FROM employees ORDER BY department_id, job_title;SELECT WHERE Clause department_id, job_title FROM employees WHERE department_id = 20;

Options A and B correctly retrieve unique combinations of department ID and job title. Option C retrieves all combinations but orders them without filtering duplicates.

Q24

Multiple Choice

Which SQL code snippet demonstrates how to use WHERE Clause with COUNT to find the number of unique job titles in the 'employees' table in Oracle?

SQL Code

SELECT COUNT(WHERE Clause job_title) AS unique_jobs
FROM employees;

SELECT COUNT(job_title) AS total_jobs
FROM employees;

SELECT COUNT(WHERE Clause job_title)
FROM employees
WHERE department_id = 10;

SELECT COUNT(WHERE Clause job_title) AS unique_jobs FROM employees; SELECT COUNT(job_title) AS total_jobs FROM employees; SELECT COUNT(WHERE Clause job_title) FROM employees WHERE department_id = 10;SELECT WHERE Clause COUNT(job_title) FROM employees;

Options A and C correctly use WHERE Clause with COUNT to find the number of unique job titles. Option B counts all job titles without filtering duplicates.

Q25

Multiple Choice

Which SQL code snippet uses WHERE Clause to retrieve unique city names from the 'locations' table in Oracle?

SQL Code

SELECT WHERE Clause city
FROM locations;

SELECT city
FROM locations
GROUP BY city;

SELECT WHERE Clause city
FROM locations
WHERE country_id = 'US';

SELECT WHERE Clause city FROM locations; SELECT city FROM locations GROUP BY city; SELECT WHERE Clause city FROM locations WHERE country_id = 'US';SELECT WHERE Clause city FROM locations;

Options A and C correctly retrieve unique city names. Option A retrieves all unique cities, while Option C filters by country before applying WHERE Clause.

Q26

Multiple Choice

Which SQL code snippet demonstrates advanced usage of WHERE Clause to retrieve unique combinations of employee names and their departments in Oracle?

SQL Code

SELECT WHERE Clause first_name, last_name, department_id
FROM employees;

SELECT first_name, last_name, department_id
FROM employees
GROUP BY first_name, last_name, department_id;

SELECT WHERE Clause first_name, last_name
FROM employees
WHERE department_id > 10;

SELECT WHERE Clause first_name, last_name, department_id FROM employees; SELECT first_name, last_name, department_id FROM employees GROUP BY first_name, last_name, department_id; SELECT WHERE Clause first_name, last_name FROM employees WHERE department_id > 10;SELECT WHERE Clause first_name, department_id FROM employees;

Options A and B correctly retrieve unique combinations of employee names and their departments. Option C retrieves unique names but filters by department.

Q27

Multiple Choice

Which SQL code snippet uses WHERE Clause to retrieve unique job titles from the 'employees' table where the salary is above a certain threshold in Oracle?

SQL Code

SELECT WHERE Clause job_title
FROM employees
WHERE salary > 50000;

SELECT job_title
FROM employees
WHERE salary > 50000
GROUP BY job_title;

SELECT WHERE Clause job_title
FROM employees
WHERE salary > 100000;

SELECT WHERE Clause job_title FROM employees WHERE salary > 50000; SELECT job_title FROM employees WHERE salary > 50000 GROUP BY job_title; SELECT WHERE Clause job_title FROM employees WHERE salary > 100000;SELECT WHERE Clause job_title FROM employees WHERE salary > 50000;

Options A and C correctly retrieve unique job titles where the salary is above a certain threshold. Option B retrieves job titles using GROUP BY.

Q28

Multiple Choice

Which SQL code snippet demonstrates the advanced use of WHERE Clause to retrieve unique customer names and order dates from the 'orders' table in Oracle?

SQL Code

SELECT WHERE Clause customer_name, order_date
FROM orders;

SELECT customer_name, order_date
FROM orders
GROUP BY customer_name, order_date;

SELECT WHERE Clause customer_name, order_date
FROM orders
WHERE order_date > SYSDATE - 30;

SELECT WHERE Clause customer_name, order_date FROM orders; SELECT customer_name, order_date FROM orders GROUP BY customer_name, order_date; SELECT WHERE Clause customer_name, order_date FROM orders WHERE order_date > SYSDATE - 30;SELECT WHERE Clause order_date FROM orders WHERE customer_name IS NOT NULL;

Options A and C correctly retrieve unique customer names and order dates. Option C includes a filter on order dates.

Q29

Multiple Choice

Which SQL code snippet uses WHERE Clause to retrieve unique product IDs from the 'order_items' table where the quantity is above a certain number in Oracle?

SQL Code

SELECT WHERE Clause product_id
FROM order_items
WHERE quantity > 10;

SELECT product_id
FROM order_items
WHERE quantity > 10
GROUP BY product_id;

SELECT WHERE Clause product_id
FROM order_items
WHERE quantity > 50;

SELECT WHERE Clause product_id FROM order_items WHERE quantity > 10; SELECT product_id FROM order_items WHERE quantity > 10 GROUP BY product_id; SELECT WHERE Clause product_id FROM order_items WHERE quantity > 50;SELECT WHERE Clause product_id FROM order_items WHERE quantity > 10;

Options A and C correctly retrieve unique product IDs where the quantity is above a certain number. Option B retrieves product IDs using GROUP BY.

Q30

Multiple Choice

Which SQL code snippet demonstrates the certification-level use of WHERE Clause to find the number of unique customers who placed orders in the last month in Oracle?

SQL Code

SELECT COUNT(WHERE Clause customer_id) AS unique_customers
FROM orders
WHERE order_date > SYSDATE - 30;

SELECT WHERE Clause customer_id
FROM orders
WHERE order_date > SYSDATE - 30;

SELECT COUNT(WHERE Clause customer_id)
FROM orders WHERE order_date > SYSDATE - 30;

SELECT COUNT(WHERE Clause customer_id) AS unique_customers FROM orders WHERE order_date > SYSDATE - 30; SELECT WHERE Clause customer_id FROM orders WHERE order_date > SYSDATE - 30; SELECT COUNT(WHERE Clause customer_id) FROM orders WHERE order_date > SYSDATE - 30;SELECT WHERE Clause COUNT(customer_id) FROM orders WHERE order_date > SYSDATE - 30;

Options A and C correctly use WHERE Clause to find the number of unique customers who placed orders in the last month. Option B retrieves the unique customer IDs without counting them.

Oracle Database Quiz Questions