Tag: databases

Questions Related to databases

What is ACID property?

technology databases

  1. Atomicity,Consistency,Isolation and Durability

  2. Atomicity,Concurrently,Isolation,Durability

  3. Atomicity,Consistency,Incremental,Durability

  4. Atomicity,Concurrently,Incremental,Durability

Show answer
Correct Option: A

In which scenario would index be most useful?

technology databases

  1. The indexed column is declared as NOT NULL

  2. The indexed columns are used in the FROM clause

  3. The indexed columns are part of an expression

  4. The indexed column contains a wide range of values

Show answer
Correct Option: D
Explanation:

To answer this question, the user needs to know what an index is and how it works.

An index is a data structure that improves the speed of data retrieval operations on a database table. It does this by providing a quick lookup mechanism for finding rows that match certain column values in the table. Indexes are most useful when searching large tables for a specific value or set of values.

Now, let's go through each option and explain why it is right or wrong:

A. The indexed column is declared as NOT NULL: This option is not necessarily the most useful scenario for an index. Declaring a column as NOT NULL simply means that the column cannot contain NULL values. While this may improve data integrity, it does not necessarily make an index more useful.

B. The indexed columns are used in the FROM clause: This option is not necessarily the most useful scenario for an index, either. Using indexed columns in the FROM clause can help improve query performance by allowing the database to retrieve only the necessary rows. However, it does not necessarily make the index more useful than other scenarios.

C. The indexed columns are part of an expression: This option can be useful for an index. When indexed columns are part of an expression, the database can still use the index to search for values that match the expression. This can help improve query performance.

D. The indexed column contains a wide range of values: This option is the most useful scenario for an index. When a column contains a wide range of values, it can be difficult for the database to search through all the values to find the ones that match a specific criteria. However, if the column is indexed, the database can use the index to quickly find the values that match the criteria, which can greatly improve query performance.

Therefore, the correct answer is:

The Answer is: D

Which clause would you use in a SELECT statement to limit the display to those employees whose salary is greater then 5000?
technology databases

  1. ORDER BY SALARY > 5000

  2. GROUP BY SALARY > 5000

  3. HAVING SALARY > 5000

  4. WHERE SALARY > 5000

Show answer
Correct Option: D
Explanation:

To solve this question, the user needs to know the basic syntax of a SELECT statement in SQL, including the purpose of each clause.

The WHERE clause is used to filter the rows returned by a query based on specified conditions. In this case, we want to limit the display to only those employees whose salary is greater than 5000. Therefore, the correct answer is:

The Answer is: D. WHERE SALARY > 5000

Option A, ORDER BY SALARY > 5000 is incorrect because the ORDER BY clause is used to sort the rows returned by a query in ascending or descending order based on a specified column. It is not used to filter rows based on specific conditions.

Option B, GROUP BY SALARY > 5000 is incorrect because the GROUP BY clause is used to group the rows returned by a query based on one or more columns. It is not used to filter rows based on specific conditions.

Option C, HAVING SALARY > 5000 is incorrect because the HAVING clause is used to filter the rows returned by a query based on conditions that involve aggregate functions, such as SUM, COUNT, AVG, MAX, and MIN. It is not used to filter rows based on specific conditions.

When should you create a role? (Choose two)
technology databases

  1. To simplify the process of creating new users using the CREATE USER xxx IDENTIFIED by yyy statement

  2. To grant a group of related privileges to a user

  3. When the number of people using the database is very high

  4. To simplify the process of granting and revoking privileges

Show answer
Correct Option: C,D

Which four are correct guidelines for naming database tables? (Choose four)

technology databases

  1. Must begin with either a number or a letter

  2. Must be 1-30 characters long

  3. Should not be an Oracle Server reserved word

  4. Must contain only A-Z, a-z, 0-+, _, *, and #.

  5. Must contain only A-Z, a-z, 0-9, _, $, and #.

  6. Must begin with a letter

Show answer
Correct Option: B,C,E,F

AI Explanation

To answer this question, you need to understand the guidelines for naming database tables. Let's go through each option to understand why it is correct or incorrect:

Option A) Must begin with either a number or a letter - This option is incorrect because database table names can begin with either a number or a letter.

Option B) Must be 1-30 characters long - This option is correct because database table names typically have a length restriction, and it is common for them to be 1-30 characters long.

Option C) Should not be an Oracle Server reserved word - This option is correct because it is important to avoid using Oracle Server reserved words as table names to prevent conflicts and confusion.

Option D) Must contain only A-Z, a-z, 0-+, _, *, and # - This option is incorrect because database table names can typically contain more characters than just A-Z, a-z, 0-+, _, *, and #.

Option E) Must contain only A-Z, a-z, 0-9, , $, and # - This option is correct because database table names generally allow a combination of letters (A-Z, a-z), numbers (0-9), underscore (), dollar sign ($), and hash (#).

Option F) Must begin with a letter - This option is correct because database table names typically begin with a letter.

The correct answers are B, C, E, and F. These options are correct because they follow the guidelines for naming database tables.

Which operator can be used with a multiple-row subquery

technology databases

  1. =

  2. LIKE

  3. BETWEEN

  4. NOT IN

  5. IS

  6. <>

Show answer
Correct Option: D

You need to perform certain data manipulation operations through a view called EMP_DEPT_VU, which you previously created. You want to look at the definition of the view (the SELECT statement on which the view was create.) How do you obtain the definition of the view

technology databases

  1. Use the DESCRIBE command in the EMP_DEPT VU view

  2. Use the DEFINE VIEW command on the EMP_DEPT VU view

  3. Use the DESCRIBE VIEW command on the EMP_DEPT VU view

  4. Query the USER_VIEWS data dictionary view to search for the EMP_DEPT_VU view

  5. Query the USER_SOURCE data dictionary view to search for the EMP_DEPT_VU view

  6. Query the USER_OBJECTS data dictionary view to search for the EMP_DEPT_VU view

Show answer
Correct Option: D

Which two are character manipulation functions? (Choose two.)
technology databases

  1. TRIM

  2. REPLACE

  3. TRUNC

  4. TO_DATE

  5. MOD

  6. CASE

Show answer
Correct Option: A,B

Which three statements correctly describe the functions and use of constraints? (Choose three.)

technology databases

  1. Constraints provide data independence

  2. Constraints make complex queries easy

  3. Constraints enforce rules at the view level

  4. Constraints enforce rules at the table level

  5. Constraints prevent the deletion of a table if there are dependencies

  6. Constraints prevent the deletion of an index if there are dependencies

Show answer
Correct Option: C,D,E

AI Explanation

To answer this question, let's go through each option to understand why it is correct or incorrect:

Option A) Constraints provide data independence - This option is incorrect because constraints do not provide data independence. Data independence refers to the ability to modify the schema definition without affecting the application programs that use the database. Constraints, on the other hand, are used to enforce rules and maintain data integrity.

Option B) Constraints make complex queries easy - This option is incorrect because constraints do not make complex queries easy. Constraints are used to enforce rules and maintain data integrity, but they do not directly impact the complexity of queries.

Option C) Constraints enforce rules at the view level - This option is correct. Constraints can be defined at the view level to enforce rules on the data displayed by the view. This ensures that only valid data is shown to the users.

Option D) Constraints enforce rules at the table level - This option is correct. Constraints are commonly defined at the table level to enforce rules on the data stored in the table. This ensures that only valid data is stored in the table.

Option E) Constraints prevent the deletion of a table if there are dependencies - This option is correct. Constraints can be used to define dependencies between tables. If there are dependencies, such as foreign key constraints, a table cannot be deleted unless the dependencies are resolved first.

Option F) Constraints prevent the deletion of an index if there are dependencies - This option is incorrect. Constraints do not prevent the deletion of an index. Indexes are used to improve query performance and do not have dependencies like tables.

Therefore, the correct statements about the functions and use of constraints are:

C) Constraints enforce rules at the view level D) Constraints enforce rules at the table level E) Constraints prevent the deletion of a table if there are dependencies

You define a multiple-row subquery in the WHERE clause of an SQL query with a comparison operator "=". What happens when the main query is executed?

technology databases

  1. The main query executes with the first value returned by the subquery

  2. The main query executes with the last value returned by the subquery

  3. The main query executes with all the values returned by the subquery

  4. The main query fails because the multiple-row subquery cannot be used with the comparison operator

  5. You cannot define a multiple-row subquery in the WHERE clause of a SQL query

Show answer
Correct Option: D