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Consider the relation Emp-Dept with SSn as key ...

  • Q.

    Consider the relation Emp-Dept with SSn as key

    Ename

    SSn

    EAddr

    Dept.

    No

    Dept.

    Name

    Dept.

    Manager

    SSn

     

    Which of the following is (are) invalid operation(s)?

    a) Inserting an employee without name and address

    b) Inserting an employee with only SSn

    c) Inserting a department with no employee

    d) Inserting an employee without SSn

  • filter_dramaExplanation
    Answer is : B

    Concept:

    • Here employee and department both table are merged into one table so right most SSn id is foreign key and second entry from left side is key of employee table.


    Statement a:

     Inserting an employee without name and address, is a valid statement because only SSn which is key should not be NULL other entries can be NULL.

    Statement b:

    Inserting an employee with only SSn, is a valid statement because only SSn which is key should not be NULL and here SSn is not NULL so valid statement

    Statement c:

    Inserting a department with no employee is a valid statement because foreign key can have NULL value.

    Statement d:

    Inserting an employee without SSn is not a valid statement because SSn employee id cannot be NULL

    So option 2 is the correct answer.

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Similar Questions

  • 1.

     Which of the following statements best describes the main reasons for normalizing relational database?

    I. To achieve physical data independence. 

    II. To remove data anomalies (insertion, update, deletion, anomalies). 

    III.  To save space on Disk. 

  • filter_dramaExplanation
    Answer is : B

    Concept:

    Normalization is the process by which we can decompose or divide any relation into more than one relation to remove anomalies in a relational database.

    Explanation:

    Normalization is a step by step process and each step in this is known as normal form. It is a reversible process.

    Properties of normalization:

    1) Remove different anomalies

    2) Decomposition must be lossless

    3) To save space on disk

    4) Reduce data redundancy

    5) Preserve necessary dependency

    Various normal forms are 1Nf, 2NF, 3NF, BCNF, 4NF and 5NF.

  • 2.

    Which of the following statements are true about the database?

    Statement 1: Each attribute in relation has a unique name.

    Statement 2:  No attribute can have many data values in one tuple.

  • filter_dramaExplanation
    Answer is : C

    The correct answer is option 3.

    Concept:

    Statement 1: Each attribute in relation has a unique name.

    True, Attributes in relational databases are the defining characteristics or properties that describe all entries belonging to a specific category and are applied to all cells in a column. Each attribute or column in relation has a unique name. The rows, on the other hand, are referred to as tuples, and they contain data sets that have been applied to a single entity in order to uniquely identify each item.

    Statement 2:  No attribute can have many data values in one tuple.

    True, No attribute can have many data values in one tuple because if an attribute can store multiple values then that database can not fails normalization. For example, A student relation has some attributes like student id, student name, student phone number and etc. An attribute student phone number can not store more than one contact number. 

    Hence the correct answer is Both statement 1 and statement 2.

  • 3.

    If the message contains only one bit and network contains a single link, and then latency corresponds to the _______

  • filter_dramaExplanation
    Answer is : D

    The amount of time taken to transmit a unit of data is called transmission time.

    Propagation delay corresponds to how long it takes a message to travel from one end of a network to the other.

    Queuing time is the time needed for each intermediate or end device to hold a message before it can be processed.

    If the message contains only one bit and we are talking about a single link (as opposed to a whole network), then the Transmit and Queue and processing time terms are not relevant, and latency corresponds to the propagation delay only.
  • 4.

    Consider the following statements regarding key -

    (I) A super key is an attribute or combination of attributes that uniquely identify records in an RDBMS table.

    (II) A candidate key is a subset of a super key.

    (III) All super keys are candidate keys but vice versa is not true.

  • filter_dramaExplanation
    Answer is : D

    The correct answer is option 1.

    Concept:

    Statement 1: A super key is an attribute or combination of attributes that uniquely identify records in an RDBMS table.

    True, A super key, or just key, is a combination of every attribute that may be used to specifically identify rows (or tuples) in a database. This indicates that a superkey may contain additional information that isn't required for uniquely identifying table rows.

    Statement 2: A candidate key is a subset of a super key.

    True, A Candidate key is a subset of Super keys and is clear of any unnecessary attributes that are not essential for tuple identification. For all tuples, the Candidate key value is distinct and non-null. Additionally, each table must include at least one Candidate key.

    Statement 3: All super keys are candidate keys but vice versa is not true.

    False, Candidate keys are a subset of Super keys. They contain only those attributes which are required to uniquely identify tuples. All Candidate keys are Super keys. But the vice-versa is not true.

    Hence the correct answer is (I) and (II) are true.

  • 5. Which of the following provides a mechanism for retrieving emails from a remote server for a mail recipient?
  • filter_dramaExplanation
    Answer is : A

    The correct answer is option 1.

    Key Points POP stands for Post Office Protocol. It provides a standard mechanism for retrieving emails from a remote server for a mail recipient.  In simple terms, a user who wants to receive emails but does not have a permanent connection to the internet uses a POP client to pull emails from the POP server.

    Hence the correct answer is POP server.

    Additional Information

    • SMTP stands for Simple Mail Transfer Protocol, and SMTP server is an application used by mail servers to send, receive, and/or relay outgoing mail between email senders and receivers.
    • Database servers are networked computers on a network dedicated to database storage and data retrieval from the database. The database server is a key component in a client/server computing environment. It holds the database management system (DBMS) and the databases.

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