DBMS Quizz

Which command is used to remove a relation from an SQL?

• Drop table

• Delete

• Purge

• Remove

Answer explanation

Explanation: Delete command is used to delete the existing record from the table. The drop table deletes the whole structure of the relation. Purge removes the table which cannot be obtained again.

Which of the following is not a DDL command?

• TRUNCATE

• ALTER

• CREATE

• UPDATE

Answer explanation

DDL commands are used to define the structure of the database, table, schemas, etc. It enables us to perform the operations like CREATE, DROP, ALTER, RENAME, and TRUNCATE schema objects.

An UPDATE command is used for managing the data stored in a database. It is an example of a DML command that also includes the INSERT and DELETE commands.

Which of the following are TCL commands?

• COMMIT and ROLLBACK

• UPDATE and TRUNCATE

• SELECT and INSERT

• GRANT and REVOKE

Answer explanation

TCL stands for Transaction Control Commands used for managing the changes made by DML commands like INSERT, DELETE, and UPDATE. The TCL commands are automatically committed in the database; that's why we cannot use them directly while creating tables or dropping them.

Which statement is used to delete all rows in a table without having the action logged?

• DELETE

• REMOVE

• DROP

• TRUNCATE

Answer explanation

TRUNCATE statement removes all rows in a table without logging the individual row deletions. It uses fewer system and transaction log resources, which makes its execution fast. This statement is similar to the DELETE statement without the WHERE clause.

SQL Views are also known as

• Simple tables

• Virtual tables

• Complex tables

• Actual Tables

Answer explanation

A view is also known as a virtual table because it contains rows and columns similar to a real table. It shows the table interface but cannot be stored in a database.

How many Primary keys can have in a table?

• Only 1

• Only 2

• Depends on no of Columns

• Depends on DBA

Answer explanation

The primary key can consist of a single or combination of the field that uniquely identifies each record in a table. It cannot be null or empty. A table may have duplicate columns, but it can contain only one primary key.

In which of the following cases a DML statement is not executed?

• When existing rows are modified.

• When a table is deleted.

• When some rows are deleted.

• All of the above

Answer explanation

The DML statement is used to access and manipulate the data in an existing table. Therefore, it cannot be used in table deletion.

Which data manipulation command is used to combines the records from one or more tables?

• SELECT

• PROJECT

• JOIN

• PRODUCT

Answer explanation

JOIN command is used with the SELECT statement to retrieve data from multiple tables. It must be needed whenever we want to fetch records from two or more tables.

A command that lets you change one or more field in a table is:

• INSERT

• MODIFY

• LOOK-UP

• All of the above

Answer explanation

The modify command is used to change one or more columns in the existing table. It is generally used with ALTER TABLE statement as follows.

LTER TABLE table_name MODIFY column_name column_type;

The SQL statement:

SELECT ROUND (65.726, -1) FROM DUAL;  

• is illegal

• garbage

• 726

• 70

Answer explanation

Here, the ROUND() function statement will produce the rounded result of the given number 65.726 from the left of decimal point up to 1.