DBMS Interview Questions - Part 5
Click Here - DBMS Interview Questions - Part 4
Click Here - DBMS Interview Questions - Part 3
Click Here - DBMS Interview Questions - Part 2
Click Here - For DBMS Interview Questions - Part 1
What is Super Key ?
An attribute or set of attributes that uniqueness in the database is referred to
as Super key. It is the superset of the Candidate key.
What is Candidate Key ?
A minimal set of attribute/attributes that can be used to uniquely identify
a single row in a given relation is referred to as Candidate key.
Explain Primary Key ?
DB Designer selects one of the candidate keys as a primary key for a
relationship for the purpose of identification of a tuple uniquely. It is identified
during table creation.
What is Composite Key ?
If a primary key has more than one attribute, then it is referred to as
Composite key.
Explain Foreign Key ?
A set of attributes/attributes that are used to establish and enforce a link
between data in two or more relations.
Explain Transaction?
Transaction refers to the collection of multiple statements, that are
responsible for transferring a database from one consistent state to another
consistent state.
Explain the role of views in the database?
View refers to the virtual table. We can create a view using create a view
statement.
CREATE VIEW as Select col1
FROM table1
where CONDITION;
Can a table have more than one primary key?
No
Explain Trigger ?
Triggers are defined as special kinds of stored programs, which are
automatically executed whenever a specific operation occurs in the
database server.
What are Locks ?
Locking is the mechanism to protect data integrity and ensure data
consistency during transactions. Locks are the most common cause of
blocked processes. Stronger the Isolation level, the more the chances of
blocking.
Can We Have NULL Value in Primary Key?
No
What are cursors ?
A cursor is a temporary work area created in system memory when a
An SQL statement is executed. A cursor can hold more than one row but can
process only one row at a time.
Explain different types of Locks?
Locks are broadly characterized into the following types :
Shared Locks: These locks are acquired by readers during reading
operations. In other words, these locks exist when two transactions are
granted read access. Data updation is not allowed until the shared lock is
released.
Exclusive Locks: In the exclusive lock, data items can be both reads as well
as written by the transaction. In Exclusive lock, multiple transactions do not
modify the same data simultaneously.
