DBMS Basics — Set 3
Computers · DBMS मूल बातें · Questions 21–30 of 60
What does DDL stand for in SQL?
Correct Answer: A. Data Definition Language
DDL refers to the subset of SQL commands used to define the database schema. Common DDL commands include CREATE, ALTER, and DROP. These commands help in building and modifying the structure of database objects.
Which of the following is a 'Data Manipulation Language' (DML) command?
Correct Answer: D. INSERT
INSERT is a DML command used to add new data into a table. DML commands deal with the actual data stored within the structures. Other examples of DML include UPDATE and DELETE.
What is the 'Durability' property in a DBMS transaction?
Correct Answer: A. Changes remain permanent even in case of system failure
Durability ensures that once a transaction is committed, its effects are saved permanently in non-volatile memory. Even if the system crashes or loses power, the updated data will not be lost. This is usually achieved through the use of transaction logs.
What is an 'Entity' in the Entity-Relationship (ER) model?
Correct Answer: D. A real-world object or concept
An entity is a 'thing' or 'object' in the real world that is distinguishable from other objects. Examples include a specific student, a car, or a bank account. Entities are represented as rectangles in ER diagrams.
Which SQL clause is used to filter records based on a specific condition?
Correct Answer: C. WHERE
The WHERE clause is used to extract only those records that fulfill a specified criteria. It can be used with SELECT, UPDATE, and DELETE statements. This helps in narrowing down data for precise analysis.
In database terms, what is 'Redundancy'?
Correct Answer: A. Unnecessary repetition of data
Redundancy occurs when the same piece of data is stored in two or more separate places. This can lead to inconsistencies and wasted storage space. Normalization is the primary method used to eliminate such duplication.
Which of the following is a characteristic of a 'Relational Database'?
Correct Answer: D. Data is organized in tables with rows and columns
Relational databases store information in tables that are linked by common fields. This structure allows for complex queries and ensures data integrity. It is currently the most widely used database model in the industry.
What is the function of the 'SELECT' statement in SQL?
Correct Answer: A. To retrieve data from a database
The SELECT statement is used to fetch specific data from one or more tables. It is the most frequently used command in SQL operations. The results are returned in the form of a result-set table.
Which constraint prevents the entry of null values into a column?
Correct Answer: C. NOT NULL
The NOT NULL constraint enforces a column to always contain a value. This means you cannot insert or update a record without providing data for that specific field. It is often applied to mandatory fields like 'ID' or 'Name'.
Which type of join returns all records when there is a match in either the left or right table?
Correct Answer: C. Full Outer Join
A Full Outer Join combines the results of both Left and Right outer joins. It returns all rows from both tables and fills in NULLs where matches are missing. This is useful for comprehensive data comparison between two sources.