Introduction to SQL - Database MCQ Questions and answers- Technical Aptitude

Option A: True - In SQL, the result of every query, whether it retrieves data from one or multiple tables, is structured as a table. Even if the query returns a single value, it is still considered as a one-column table. This table-like structure allows SQL to handle and manipulate data uniformly, regardless of the complexity of the query or the number of tables involved. Conclusion:
The statement "The result of every SQL query is a table" is Option A: True. Therefore, the correct answer is True.

Option A: True - The COUNT(field_name) function in SQL counts only those rows where the specified field (column) contains a non-null value. It does not count rows where the field is null. Therefore, rows with null values in the specified field are ignored in the count. Conclusion:
The statement "COUNT(field_name) tallies only those rows that contain a value; it ignores all null values" is Option A: True. Hence, the correct answer is True.

Option A: True - The SQL aggregate functions SUM, AVG, MIN, and MAX are designed to operate on numeric columns or expressions. They calculate totals, averages, minimum values, and maximum values respectively for the specified numeric data in a column. These functions are not applicable to non-numeric data types such as text or date columns.

Conclusion:
The statement "SUM, AVG, MIN, and MAX can only be used with numeric columns" is Option A: True. Hence, the correct answer is True.

Option B: False - Most companies typically maintain multiple versions of their databases for backup and recovery purposes. This practice ensures that if there are issues with the current version or data corruption occurs, they can revert to a previous version to minimize data loss and downtime. However, maintaining exactly two versions is not a strict rule; the number of versions kept may vary depending on the company's policies, needs, and the criticality of the data.

Conclusion:
The statement "Most companies keep at least two versions of any database they are using" is Option B: False. Hence, the correct answer is False.

The SELECT-FROM-WHERE format is indeed the fundamental framework of SQL SELECT statements. This structure outlines how SQL queries are typically written:
SELECT: Specifies the columns or expressions to retrieve from the database.
FROM: Specifies the table or tables from which to retrieve the data.
WHERE: Filters the rows returned by specifying conditions that must be met.
This format provides a structured way to query data from relational databases using SQL.

Conclusion:
The statement "The format SELECT-FROM-WHERE is the fundamental framework of SQL SELECT statements" is Option A: True. Hence, the correct answer is True.

Indexes in SQL can indeed be created or dropped at any time during the lifecycle of a database. Indexes are used to improve the speed of data retrieval operations by providing quick access paths to data based on the indexed columns. They can be added to speed up queries or removed if they are no longer necessary or if they degrade performance for certain operations.

Conclusion:
The statement "Indexes may be created or dropped at any time" is Option A: True. Hence, the correct answer is True.

The SQL statement SELECT Number1 + Number2 AS Total FROM NUMBER_TABLE; performs arithmetic addition on the columns Number1 and Number2 for each row in the NUMBER_TABLE. The result of each addition operation is stored in a new column named Total.

Conclusion:
The statement "The SQL statement: SELECT Number1 + Number 2 AS Total FROM NUMBER_TABLE; adds two numbers from each row together and lists the results in a column named Total" is Option A: True. Hence, the correct answer is True.

The ORDER BY clause in SQL is used to sort the result set returned by a SELECT statement. It sorts the rows in ascending or descending order based on one or more columns specified in the ORDER BY clause.

Conclusion:
The statement "ORDER BY can be combined with the SELECT statements" is Option A: True. Hence, the correct answer is True.

Data Manipulation Language (DML) commands in SQL are used to manipulate data in the database, not to define the database structure. DML commands include INSERT, UPDATE, DELETE, and SELECT (when used to retrieve data).

Conclusion:
The statement "Data manipulation language (DML) commands are used to define a database, including creating, altering, and dropping tables and establishing constraints" is Option B: False. Hence, the correct answer is False.

Option B: False
Scalar aggregates refer to a single value returned from an SQL query that includes an aggregate function like COUNT, SUM, AVG, MIN, or MAX. These functions operate on a set of values and return a single result.

Conclusion:
The statement "Scalar aggregate are multiple values returned from an SQL query that includes an aggregate function" is Option B: False. Hence, the correct answer is False.